GST compliance for retailers: build in-house or buy

Date: 2026-10-03
Status: first draft from desk research, before the team's own shortlist is added
Scope: Trendzo as a software platform that connects retailers and shoppers (retailers are the suppliers; Trendzo is the mediator).
Not tax advice. Legal points come from CBIC-linked and secondary sources (cbic-gst.gov.in and incometaxindia.gov.in could not be read directly). A chartered accountant (CA) should confirm everything in section 8 before decisions are made.

1. Summary and recommendation

Trendzo has obligations of its own, not just the retailers'. Shoppers pay through Trendzo's checkout (Razorpay), so Trendzo is an e-commerce operator (ECO) that collects the money. That makes it responsible for TCS at 0.5% per retailer, a monthly GSTR-8 return, TDS at 0.1% on retailer payouts and its own commission invoices. The retailer remains the supplier and owes the tax invoice to the shopper.
Most of the building blocks already exist in the code: invoices, gap-free numbering, credit notes, payout maths, month close, a GSTR-1 B2C CSV and a TCS CSV. But several are wrong or unfinished (placeholder issuer GSTIN on commission invoices, GSTR-3B returns an error, no GSTR-8, no TDS data, month close fails from the screen).
Do not buy a full GST platform yet. Public pricing for the big suites starts at roughly ₹90,000 a year and runs to ₹3.6-6 lakh a year, and they mainly solve a problem Trendzo does not have yet: retailers above ₹5 crore turnover needing e-invoice and e-way bill for B2B sales.
Recommended path (hybrid):
1. Fix and finish the in-house ledger and documents first. It is the data every filing depends on.
2. File GSTR-8 with the free government offline utility, or a CA (about ₹2,000-4,000 a month).
3. Verify retailer GSTINs with a cheap API (about ₹0.40-0.72 a check).
4. Use a filing service or desktop tool for the TDS return (about ₹2,250 a quarter managed).
5. Revisit a GST API provider once retailers need e-invoice or e-way bill, or when manual filing becomes the bottleneck. - Billing products (added after review): Zoho, Refrens, Chargebee and peers were checked (section 5.8). They fit one job well: Trendzo's own commission and subscription invoices (one issuer). They do not fit retailer-to-shopper invoices for many retailers: none is truly multi-tenant, so each retailer would need its own paid account or key. - What changes the answer: whether retailers or Trendzo collect the shopper's money, how many retailers are above ₹5 crore, and how fast the legal rules keep changing (five changes in about two years, section 4).

2. Where Trendzo sits as a mediator

Trendzo supplies software and takes a commission. The goods are sold by the retailer. The table shows who owes what, assuming Trendzo's checkout collects the shopper's payment.

Obligation	Owed by	Frequency	Trendzo's role
Tax invoice to the shopper (goods)	Retailer	Per order	May generate it on the retailer's behalf in the retailer's name and GSTIN, with a written authorisation and a separate numbering series per GSTIN. The retailer stays liable.
Bill of supply (composition dealers, exempt goods)	Retailer	Per order	Same: generate on behalf, using the right document type per retailer.
Credit note on a return	Retailer	Per return	Generate on behalf; also net returns in GSTR-8.
Commission, platform fee, delivery fee invoice	Trendzo	Per order or per month (within 30 days)	Issue under Trendzo's own GSTIN, 18% GST. The place of supply for a registered retailer is the retailer's location.
TCS under GST s.52 at 0.5% of each retailer's net taxable supplies (returns netted)	Trendzo	Monthly	Collect from the retailer payout; track per retailer GSTIN.
GSTR-8 return	Trendzo	By the 10th of the next month	Prepare and file; also the annual statement (GSTR-9B). Retailers then accept the TCS credit.
TDS under income tax, old s.194-O (now s.393(1) of the Income-tax Act 2025) at 0.1%	Trendzo	Deduct at credit or payment; quarterly return	Deduct from payouts; file Form 140 (earlier 26Q); issue Form 131 (earlier 16A). Resident individuals or HUFs up to ₹5 lakh a year who give PAN or Aadhaar are exempt.
E-invoice (IRN)	Retailer, only if its annual turnover is above ₹5 crore	Per B2B invoice	May generate on the retailer's behalf. B2C invoices are out of scope, so most retailers need none.
E-way bill	Consignor (retailer)	Per consignment above ₹50,000	May fill Part A with authorisation.
Registration of sellers	Retailer	Once	Enforce: compulsory when the ECO collects TCS, except small intra-state sellers with an enrolment ID.
Records for 72 months, edit log	All parties	Continuous	Keep records; answer officer requests within 15 working days.

Points that matter for design:

Section 9(5), where the platform pays the GST itself, does not cover goods or fashion. It applies to services such as restaurants and, since 22 Sep 2025, local delivery by unregistered riders at 18%. If Trendzo's riders are unregistered, the delivery fee needs a CA's view.
Composition dealers may sell goods through an ECO (since 1 Oct 2023), but Trendzo must block their inter-state orders, collect TCS and report them in GSTR-8.
Small unregistered sellers can sell only inside their own state, using an enrolment ID. No TCS on them, but they appear in GSTR-8 Table 3.1. They cannot charge GST. There is no exemption for small inter-state sellers of goods. A single-state registration scheme is on the GST Council agenda for 7 Oct 2026.
If retailers collected the shoppers' money directly, there would be no TCS and no GSTR-8, but TDS would still apply. That is a design choice with large consequences, so it needs a CA's confirmation.

3. What Trendzo already builds in-house

From a read-only review of the backend and web portal:

Exists and works

Tax invoices to shoppers on delivery, supplementary invoices when a held item is kept, credit notes on successful refunds, and counter-sale invoices or bills of supply in POS.
Per-order commission invoices (SAC 9985 at 18%) issued on delivery.
Gap-free numbering per legal entity, financial year and series, with PDFs stored.
Payout maths: commission, 18% GST on commission, TCS, refunds, holds and adjustments.
Month close that writes statements, a GSTR-1 B2C CSV and a TCS CSV; a retailer GST summary and HSN summary with CSV export.

Known defects and gaps

GSTR-3B is not built (the endpoint returns an error); there is no GSTR-8; there is no TDS ledger and no Form 140 or 131 data.
The commission invoice issuer is the placeholder PLATFORM-GSTIN; it uses the retailer's numbering series; the CGST/SGST versus IGST choice uses the shopper's state; commission is not reversed on returns.
The month-close button sends a period format the API rejects, so it fails from the screen; closing does not lock the period.
TCS defaults to 1% where the law says 0.5%, is added to the shopper's invoice total although checkout does not charge it, and is calculated on different bases in the invoice and the payout.
Composition dealers get a tax invoice online; buyer GSTIN is never captured, so no B2B; shoppers cannot fetch their invoices.
GSTIN is checked for length only. No e-invoice and no e-way bill.
A failed invoice is only logged; nothing retries. The retailer statement PDF button is disabled and its holds and TCS figures show zero.

4. What a full in-house build still needs

Capability	Gap to close	Size
Seller-wise TCS ledger	Net taxable value per retailer GSTIN per month, returns netted, CGST/SGST/IGST split, one rate and one base	M
GSTR-8 file	Table 3 and 3.1 data in the portal's upload format, plus amendments	M
TDS ledger and Form 140 / 131 data	Per PAN, ₹5 lakh check, quarterly return file, certificate data	M
Per-retailer GSTR-1 and GSTR-3B data	Per GSTIN, B2B and B2C, credit notes with tax split	M-L
Commission invoice fixes	Real platform GSTIN, platform series, correct place of supply, reversal on return	S-M
Document type per retailer	Bill of supply for composition dealers; buyer GSTIN for B2B	S-M
Month close and scheduling	Fix the period format, lock periods, run on a schedule	S
GSTIN verification	Checksum plus live lookup (almost always bought as an API)	S
E-invoice and e-way bill	Only for retailers above ₹5 crore or large consignments; almost always bought through a GST API provider	L if built
Filing calendar, health dashboard, CA access	Reminders, missing HSN or bad GSTIN alerts, read-only CA role	S-M

Sizes are relative effort (S under a week, M 1-3 weeks, L over 3 weeks, for one developer who knows the code), not estimates.

Rules keep changing, and each change is engineering and CA time:

TCS rate cut from 1% to 0.5% (10 Jul 2024).
TDS rate cut from 1% to 0.1% (1 Oct 2024).
Local delivery by unregistered riders brought under s.9(5) at 18% (22 Sep 2025).
Credit notes tied to the buyer's input credit reversal through the Invoice Management System (1 Oct 2025).
Income-tax Act 2025 (1 Apr 2026): old section 194-O became s.393(1); Form 26Q became Form 140 and Form 16A became Form 131.
Pending: a single-state registration scheme for small ECO sellers (Council meeting 7 Oct 2026).

5. Third-party options by layer

All prices were read on public pages on 2026-10-03 and are in rupees. "Quote on request" means no public price. Whether prices include GST was often not stated.

5.1 GSTIN, PAN and bank verification

Appyflow: GSTIN lookup, ₹0.50 a request (₹0.40 if a recharge is above ₹1,000), credits never expire, 50 free requests. https://appyflow.in/verify-gst/
gstinapi.com / gstinapi.in: ₹0.50 a check, ₹0.40 at 2,500+ credits; the second site quotes ₹0.40-0.80 and 100 free lookups (its comparison page is self-promotional). https://gstinapi.com/pricing
GSTZen GST Validator: ₹3,500 a year for 5,000 calls, ₹5,000 for 10,000, ₹8,250 for 25,000. https://gstzen.in/gst-validator-api-pricing-details
Eko EPS: GSTIN from ₹0.72 a verification; PAN and bank too. https://eps.eko.in/products/gst-verification-api
Quote on request: Cashfree Secure ID (GSTIN, PAN, bank penny-drop; ₹100 trial credits), Signzy (₹5,000 sandbox credits), Surepass, Karza (Perfios), IDfy, Attestr. Setu offers bank verification; a "₹3 per verification" figure appeared only in search snippets, so it is not verified.
GSTN enrolment-ID checks for unregistered sellers are available only through a GSP.
Verdict: buy. At a few hundred retailers the cost is under ₹1,000 a year.

5.2 E-invoice (IRN) and e-way bill APIs

NIC portals: free, but a direct API is for very large taxpayers only (the threshold is stated as ₹100 crore on one NIC page and ₹500 crore elsewhere). Everyone else goes through a GSP. https://einv-apisandbox.nic.in/onboarding.html
IRIS IRP-6 and Cygnet IRP-3: government-authorised e-invoice portals; basic generation free (IRIS premium services "to be announced"). https://einvoice6.gst.gov.in/content/pricing-plan/
GSTZen: e-invoice 18 paise an invoice with a ₹50,000 a year minimum (invoices kept 10 days), or 50 paise with a ₹25,000 minimum (kept 7 years); signing certificate ₹15,000 a year. E-way bill 18 paise with a ₹50,000 minimum per GSTIN, or 35 paise with ₹25,000 per GSTIN. https://gstzen.in/e-invoicing-api-integration-pricing
Adaequare: IRN 0.25 a transaction, IRN with e-way bill 0.40, custom payloads 0.80, plus GSTR-1 transfer 1.50. Its page had an expired certificate when read, and the currency symbol did not display, so INR is assumed. https://ugsp.adaequare.com/e-invoice-api
Verdict: buy, only when retailers above ₹5 crore sell to businesses or ship large consignments. Prefer per-transaction pricing; avoid per-GSTIN minimums with many small retailers.

5.3 GST suites and API providers (GSPs)

ClearTax (Clear): suite "starting at ₹7,777 a month"; API per-call price on request. Says it is a GSP/ASP. Each GSTIN needs its own NIC API credentials. https://cleartax.in/s/e-invoicing-gst-compliance-solution/
Adaequare: GST API plans ₹50,000 a month including 2,00,000 calls, or ₹30,000 a month including 1,00,000 calls; "Enriched" plan ₹50,000 a month including 500 GSTINs. https://ugsp.adaequare.com/gst-apis
WhiteBooks: two pages conflict: "₹5,999 to ₹24,999" and "startup tier from ₹14,999 a month". Explicit multi-GSTIN support with delegated consent. https://whitebooks.in/about/pricing/
Quote on request: Masters India (also a GSP), MasterGST (Tera Software), IRIS GSP, WeP, TaxPro GSP, Cygnet GSP.
Vayana: not verified; a reseller lists ₹40,000-75,000 a year plus integration fees.
Sandbox.co.in (Quicko): 200+ APIs including GSTIN, returns, e-invoice, PAN and bank; a technology provider, not a GSP; 14-day trial; plan prices are a dynamic calculator and were not readable. https://sandbox.co.in/pricing
India Compliance (ERPNext): open-source GST app, free on Frappe Cloud; credit price not verified. https://indiacompliance.app/
Verdict: defer. These matter when many retailers need returns, e-invoice and e-way bill through your platform. Ask any shortlisted provider whether it stores each retailer's credentials with consent and whether pricing is per call or per GSTIN.

5.4 GSTR-8 and TCS tools

GSTN GSTR-8 Offline Utility: free government download; you fill a CSV or Excel and upload it. Good if Trendzo exports a retailer-wise CSV each month.
Clear GST (ClearTax): GSTR-8 preparation, many GSTINs, template import, TCS challans; quote on request.
Taxilla: matches TCS to order and settlement data, seller GSTIN checks, approvals, audit logs; enterprise, quote on request. https://www.taxilla.com/blog/gstr-8-filing
IRIS Sapphire, Cygnet Tax: report GSTR-8; quote on request (Cygnet not verified, its site did not load).
Gen GST (SAG Infotech): desktop ₹5,000 install and ₹2,000 a year; online e-filing ₹25,000 and ₹10,000; all-in-one online ₹10,000 and ₹7,000, plus 18% GST. GSTR-8 appears only in a third-party listing. https://saginfotech.com/PriceCalculator.aspx
Not confirmed to support GSTR-8 for operators: Zoho Books, TallyPrime, Avalara India, Masters India (no product page), Vayana (no public endpoint).
Verdict: use the free utility or a CA now; look at Clear or Taxilla only at thousands of sellers or for API filing.

5.5 TDS (194-O) returns and certificates

Sandbox (Quicko): TDS calculation, PAN and TAN checks, Form 16A and 26Q APIs; plan price not readable. https://sandbox.co.in/tds
Gen e-TDS: ₹3,500 install and ₹1,500 a year, plus GST. https://saginfotech.com/PriceCalculator.aspx
Winman TDS: list ₹13,300; ₹7,490 only for existing Winman licence holders; the price list is undated. https://www.winmansoftware.com/files/Software_pricelist_winman.pdf
KDK Spectrum Cloud TDS: bulk Form 16/16A, TRACES fetch, Form 26Q/140; price not on the vendor page (a third party says ₹6,300 a year, not verified). https://www.kdksoftware.com/spectrum-cloud/tds/
TDSMAN: desktop and cloud editions; rupee amounts not readable. https://www.tdsman.com/pricing.asp
Managed filing: EZTax Form 140 / 26Q ₹2,249 plus GST a quarter, including Form 131 certificates (https://eztax.in/form26q-tds-return); ClearTax expert TDS from ₹2,500 for 24Q and 26Q (https://cleartax.in/tds).
Check before buying: only KDK and EZTax mention the renamed Forms 140 and 131.

5.6 Managed CA and compliance services

Patron Accounting (indicative, per its page): GSTR-8 only ₹1,999 a month per GSTIN; GSTR-8 + GSTR-1 + GSTR-3B ₹3,999 a month; reconciliation ₹2,999 a month; section 9(5) add-on ₹1,999 a month; annual return ₹4,999; annual package ₹39,999; 20% off for 5+ GSTINs. TDS 194-O is not mentioned. https://www.patronaccounting.com/gst-returns-for-e-commerce-operator
IndiaFilings, TaxBuddy: no prices shown.
Note: GSTR-8 is filed under Trendzo's own GSTIN, so "per GSTIN" here means one or two GSTINs, not one per retailer.

5.7 Payout splitting and retailer-side accounting

Cashfree Easy Split and Razorpay Route: split payments and pay vendors; reconciliation reports. Neither page says it computes TCS or TDS natively. Prices not checked. https://www.cashfree.com/docs/payments/split/billing/configuration, https://razorpay.com/route/
Zoho Books (per organisation a month, billed annually): Free; Standard ₹749; Professional ₹1,499; Premium ₹2,999; Elite ₹4,999; Ultimate ₹7,999. E-invoice and e-way bill from Standard up. API 1,000-10,000 calls a day by plan. https://www.zoho.com/in/books/pricing/
TallyPrime: Silver ₹22,500 lifetime or ₹750 a month; Gold ₹67,500 or ₹2,250 a month. Integration is XML against a running Tally install, not cloud REST (third-party source). https://tallysolutions.com/buy-tally/
Cygnet Invoicing Tool: free plan; Standard ₹9,999 a year (3,000 invoices, up to 10 GSTINs); Premium ₹14,999 (10,000 invoices, up to 20 GSTINs). https://invoicingtool.cygnettaxtech.com/pricing/
Swipe: list prices not verified. Razorpay Invoices: the API can create only non-GST invoices, so it cannot make GST invoices.
Verdict: these are for retailers to run their own books. Paying for them per retailer does not scale (see the scenario table).

What the research did not find: a public vendor case study of a marketplace; how Amazon, Flipkart, Meesho or Myntra run TCS and TDS internally (only Amazon's blog says Amazon files GSTR-8).

5.8 Billing and invoicing products (Zoho, Refrens, Chargebee and peers)

Added after the first review. Sections 5.1-5.7 are unchanged; this section adds detail and new products. Pages read 2026-10-03; prices exclude GST. Two separate jobs are in play:

Job A: Trendzo's own invoices to retailers (commission, platform fee, subscription). One issuer, recurring, B2B.
Job B: retailer-to-shopper tax invoices generated for many retailers, each under its own GSTIN.

Zoho Books

GST: tax invoice, credit note, bill of supply, delivery challan, place of supply, HSN/SAC. E-invoice (IRN) through the portal (Zoho is a GSP). E-way bill on all plans. GSTR-1 and 3B from the app. Several GSTINs through branches (a 2020 blog, updated 2024, says up to 10 depending on plan).
API and tenancy: REST with OAuth2 and an organization_id on every call, so one organisation per business. An endpoint exists to create organisations. E-invoice push, cancel and fetch endpoints exist. Webhooks only through workflow rules.
API limits: 1,000 calls a day on Free, 2,000 Standard, 5,000 Professional, 10,000 Premium and above; 100 a minute per organisation.
Price per organisation a month (monthly / annual billing): Free ₹0; Standard ₹899 / ₹749; Professional ₹1,799 / ₹1,499; Premium ₹3,599 / ₹2,999; Elite ₹5,999 / ₹4,999; Ultimate ₹9,599 / ₹7,999. Invoices a year: 1,000-5,000 on Free and Standard, 10,000 Professional, 25,000 Premium, 100,000 Elite and Ultimate.
Fit: Job A, good for one Trendzo organisation. Job B, only as one paid organisation per retailer with the retailer's OAuth consent; it is not a multi-tenant product.
Sources: https://www.zoho.com/in/books/pricing/ · https://www.zoho.com/books/api/v3/introduction/ · https://www.zoho.com/in/books/help/e-way-bill/

Zoho Billing (formerly Subscriptions)

What: recurring billing. E-way bill once GST and GSTIN are set. IRN through the portal. The marketing page claims multi-GSTIN and webhooks.
API: organisation id header on every call; 100 a minute per organisation; 1,000 calls a day on Standard and 5,000 on Premium.
Price: Enterprise is ₹24,999 per organisation a month, billed annually, plus 0.2% of monthly revenue above ₹2.5 crore (official page). Standard and Premium are not verified: the official page text is garbled, and a third-party page dated 8 Jul 2026 says Standard ₹1,499 monthly / ₹1,249 annual and Premium ₹3,499 / ₹2,999. Both are capped at 100,000 invoices a year and ₹8 crore revenue. Subscription management, dunning and hosted pages are Premium and above.
Fit: Job A, the best Zoho option for commission and SaaS billing. Job B, the same one-organisation limit as Books.
Sources: https://www.zoho.com/in/billing/enterprise/pricing/ · https://goforfiling.com/zoho-billing-pricing/

Zoho Invoice and Zoho Commerce

Zoho Invoice: free tool, 500 invoices a year and 2 users; GST invoices; no IRN endpoint seen in the API docs read. Too small for either job. https://www.zoho.com/in/invoice/pricing/
Zoho Commerce: a single-merchant storefront builder (Starter ₹99 a month on annual billing, other plans hidden); no multi-vendor or invoice API found. Not relevant. https://www.zoho.com/commerce/pricing/

Refrens

GST: credit notes, place of supply, HSN/SAC, IRN, e-way bill, GSTR-1 / 3B / 9 reports, several GSTINs in one account. Direct return filing not verified.
API: REST with JWT; the API is enabled per business by support. Creating an invoice takes the issuer's GST fields and an invoice type (invoice or bill of supply). An IRN endpoint is referenced. Credit notes through the API, rate limits and webhooks are not documented.
Marketplace pattern: a published case study (AiSensy) auto-creates a Refrens business for each reseller through the API. That is the closest thing found to what Trendzo needs, but it is still one business per retailer.
Price per business a year: Basic ₹0 (15 documents); Accounts Lite ₹5,900; Accounts Pro ₹15,000 (e-invoice and e-way bill start here); Workflows ₹22,000; Operations ₹39,000; Services on quote. The page is undated. API invoice creation is "charged" but the amount is not public.
Fit: Job A, possible but weaker on dunning and payments. Job B, workable, with a cost per retailer.
Sources: https://www.refrens.com/refrens-premium · https://www.refrens.com/api/docs/invoices/ · https://www.refrens.com/grow/reseller-invoice-api-aisensy-case-study/

Chargebee

GST: manual GST rates, a GSTIN per state, CGST/SGST/IGST split, an HSN code per plan or add-on (needed for Avalara). SEZ and export only in the primary tax profile. Marketing says IRP e-invoicing is supported, but the documentation describes a partner-led approach with no India steps. E-way bill and GSTR are not mentioned.
Multi-entity: uses a business-entity header on each API call. Enabling it is irreversible. In multi-entity, tax is limited to Avalara or TaxJar and separate tax profiles per entity are not supported.
API limits (old plan names): 150 a minute Starter, 1,000 Performance, 3,500 Enterprise.
Price, in US dollars (no INR): Flow plan $0 plus 0.80% of billed volume, or $99 plus 0.65%. Enterprise on quote, multi-entity up to 100 entities. The e-invoicing add-on is paid. At 0.80%, ₹10,00,000 of commission billed in a month would cost about ₹8,000 a month before currency conversion.
Fit: Job A, technically fine but priced in dollars and as a percentage of volume. Job B, poor: Enterprise only, a 100-entity ceiling, no tax profile per entity, no e-way bill or GSTR.
Sources: https://www.chargebee.com/pricing/ · https://www.chargebee.com/docs/billing/2.0/taxes/indian-gst · https://www.chargebee.com/docs/billing/2.0/multi-business-entity/mbe-limitations

Other billing apps and payments-led peers (supplements 5.7)

Swipe: API v2 covers invoices, returns, challans and subscriptions. IRN on creation; e-way bill needs a portal link; webhooks signed with HMAC. An API key belongs to one company; 1 request a second per key; creates are not idempotent; creating businesses through the API is undocumented. Official prices were unreadable or contradictory; third-party listings show PRO ₹2,999 per user a year up to RISE + E-Invoice ₹7,499. https://developers.getswipe.in/llms.txt
Vyapar: desktop and mobile billing with IRN, e-way bill and a multi-GSTIN claim; no public API found. Per device a year: Silver about ₹3,419 and Gold about ₹3,689 (SoftwareSuggest, 25 Jun 2026; another source says ₹3,799 and ₹4,099). Not usable for either job. https://www.softwaresuggest.com/vyapar
Razorpay Subscriptions: cards 0.9% plus a platform fee on the official pricing page (a third party says 0.99%), UPI and NACH on quote. Dashboard invoices are GST-compliant, but the API docs state that GST-compliant invoices cannot be created through the API. Route splits payments to linked accounts at 0.1% plus fees; invoices on behalf of sellers are not mentioned. https://razorpay.com/pricing/ · https://razorpay.com/docs/payments/route/
Cashfree Subscriptions: from a third-party snippet, a mandate fee of ₹7.5 and ₹7.5 per debit on card or eNACH, ₹5 or ₹15 on UPI AutoPay; no tax-invoice API found. https://www.cashfree.com/docs/partners/embedded/commissions-and-invoices
ClearTax and Masters India (invoice side): IRN and e-way bill APIs only. ClearTax says an e-commerce operator may request an IRN on a supplier's behalf, up to 10 invoices a call. They issue the IRN, not the invoice document.

Which can and cannot do GST invoices through an API

Can, with limits: Zoho Books, Zoho Billing, Refrens, Swipe, and Chargebee for tax calculation only.
Cannot: Razorpay Invoices (stated in its docs), Cashfree, Zoho Commerce, Vyapar (no public API found), and Zoho Invoice (no IRN endpoint seen).

What fits which job

Job A (Trendzo's own commission and subscription invoices): Zoho Billing Premium or Enterprise, or Zoho Books, is the cleanest fit: a tax invoice, credit notes, recurring invoices and GST returns from one place, with IRN available through the portal. Razorpay or Cashfree can collect the money but do not issue the tax document.
Job B (retailer-to-shopper invoices for many retailers): no product is truly multi-tenant. The realistic options are one account or key per retailer (Refrens, Swipe, Zoho) with a per-retailer fee, retailer consent and automated onboarding, or building the invoice in-house and adding an IRN-only API for the few retailers above ₹5 crore. In-house stays cheaper at this volume.

6. Build or buy, by capability

Capability	Recommendation	Reason
Seller-wise TCS and TDS ledger	Build	It is your own data (orders, returns, payouts). No vendor can compute it without it.
Retailer tax invoice, bill of supply, credit note	Build	Already exists; fix defects. Per-order volume and generation on the retailer's behalf are cheaper in-house.
Commission, platform and delivery fee invoices	Build	Trendzo's own documents; fix issuer, series and place of supply.
GSTR-8 file	Build the file, file via utility or CA	A CSV export is small; the free utility accepts it; a CA costs about ₹2,000-4,000 a month.
Form 140 / 131	Build the data, buy the filing	Return utilities are cheap or managed filing is about ₹2,250 a quarter.
GSTIN, PAN, bank verification	Buy	₹0.40-0.72 a check; building lookups is not worth it.
E-invoice and e-way bill	Buy, when needed	Only for retailers above ₹5 crore or consignments above ₹50,000; per-transaction API pricing.
Per-retailer GSTR-1 / GSTR-3B data	Build data, retailers or their CA file	Data export is cheap; a GSP is only needed to file through your platform.
Filing through your platform on behalf of retailers	Buy (GSP) later	Large fixed cost and credential handling; not needed to start.
Retailer bookkeeping	Retailers' choice	Do not pay per retailer.
Trendzo's own commission and subscription invoices (added)	Build now; consider buying later	Already built in-house but defective. A billing product (Zoho Billing or Books) fits well if Trendzo wants recurring billing, dunning and returns from one tool.
Retailer-to-shopper invoices through a billing product (added)	Do not buy	No product is multi-tenant; each retailer would need its own paid account or key (Zoho, Refrens, Swipe). Chargebee has no tax profile per entity.

7. Pricing comparison

7.1 Public prices found (2026-10-03)

Item	Provider	Price as published	Unit	Notes
GSTIN check	Appyflow	₹0.50 (₹0.40 over ₹1,000 recharge)	per check	50 free
GSTIN check	gstinapi.com	₹0.50 (₹0.40 at 2,500+)	per check	20 free
GSTIN check	GSTZen	₹3,500 / ₹5,000 / ₹8,250	per year for 5,000 / 10,000 / 25,000 calls
GSTIN check	Eko	from ₹0.72	per check	volume tiers by quote
E-invoice	Adaequare	0.25 (IRN), 0.40 (IRN + e-way bill)	per transaction	currency assumed INR
E-invoice	GSTZen	0.18 with ₹50,000 minimum, or 0.50 with ₹25,000 minimum	per invoice, per year	cert ₹15,000 a year
E-way bill	GSTZen	0.18 with ₹50,000, or 0.35 with ₹25,000	per bill, per GSTIN a year	per-GSTIN minimum
GST API	Adaequare	₹50,000 or ₹30,000	per month (2,00,000 or 1,00,000 calls)	currency assumed INR
GST suite	ClearTax	from ₹7,777	per month	API price on request
GST API	WhiteBooks	₹5,999-24,999 or from ₹14,999	per month	two pages conflict
GSTR-8	GSTN offline utility	free	n/a	needs your own CSV
GSTR-8	Patron Accounting	₹1,999	per month per GSTIN	indicative
GSTR-8 + 1 + 3B	Patron Accounting	₹3,999	per month	indicative
TDS return	EZTax	₹2,249 + GST	per quarter	includes Form 131
TDS return	ClearTax expert	from ₹2,500	per filing (24Q + 26Q)	period not stated
TDS software	Gen e-TDS	₹3,500 + ₹1,500 a year + GST	install, renewal	check Form 140 support
Retailer books	Zoho Books Standard	₹749	per org per month (annual billing)
Retailer books	Cygnet Invoicing Tool	₹9,999 / ₹14,999	per year for 10 / 20 GSTINs	3,000 / 10,000 invoice caps
Retailer books	Zoho Books (full ladder)	Free; ₹749; ₹1,499; ₹2,999; ₹4,999; ₹7,999 (annual billing; monthly ₹899 / ₹1,799 / ₹3,599 / ₹5,999 / ₹9,599)	per org per month	Standard to Ultimate; invoices 1,000-100,000 a year
Own billing	Zoho Billing Enterprise	₹24,999 + 0.2% of monthly revenue above ₹2.5 crore	per org per month, annual billing	official page
Own billing	Zoho Billing Standard / Premium	₹1,249 / ₹2,999 (annual)	per org per month	third-party only; official page garbled
Own billing, one business each	Refrens	₹0; ₹5,900; ₹15,000; ₹22,000; ₹39,000	per business per year (Basic to Operations)	e-invoice and e-way bill from ₹15,000; API fee not public; page undated
Own billing	Chargebee	$0 + 0.80%, or $99 + 0.65%	per month, of billed volume	USD; Enterprise on quote; e-invoicing paid add-on
Billing app	Swipe	₹2,999 to ₹7,499	per user per year	third-party only; official page unreadable
Billing app	Vyapar	about ₹3,419 / ₹3,689	per device per year	no public API found
Collection	Razorpay Subscriptions	0.9% + platform fee (cards)	per transaction	UPI and NACH on quote; no GST invoice via API
Collection	Cashfree Subscriptions	₹7.5 mandate + ₹7.5 per debit (card / eNACH)	per mandate, per debit	third-party snippet only

Quote-only: Masters India, MasterGST, IRIS, WeP, TaxPro, Cygnet GSP, Taxilla, Clear GST API, Surepass, Signzy, Karza, IDfy, Setu, Cashfree, Attestr, Sandbox plans.

7.2 What it costs at three sizes (public prices only; assumptions stated)

Assumptions: two GSTIN checks per retailer a year (at signup and a yearly re-check); GSTR-8 and TDS are filed once for Trendzo's own GSTIN, so retailer count does not change them; e-invoice and e-way bill are needed by few retailers.

Cost line	100 retailers	500 retailers	2,000 retailers
GSTIN checks, Appyflow at ₹0.50	₹100 a year	₹500 a year	₹2,000 a year
GSTIN checks, GSTZen 5,000-call pack	₹3,500 a year	₹3,500 a year	₹3,500 a year
GSTR-8 by free offline utility	₹0 plus staff time	₹0 plus staff time	₹0 plus staff time
GSTR-8 only by CA (₹1,999 a month)	₹23,988 a year	₹23,988 a year	₹23,988 a year
GSTR-8 + own GSTR-1 + 3B by CA (₹3,999 a month)	₹47,988 a year	₹47,988 a year	₹47,988 a year
TDS return, EZTax (₹2,249 a quarter, plus GST)	₹8,996 a year	₹8,996 a year	₹8,996 a year
GST API, Adaequare 100k-call plan	₹3,60,000 a year	₹3,60,000 a year	₹3,60,000 a year
GST suite, ClearTax from ₹7,777 a month	₹93,324 a year	₹93,324 a year	₹93,324 a year
If Trendzo paid retailers' books, Zoho Standard	₹8,98,800 a year	₹44,94,000 a year	₹1,79,76,000 a year
Trendzo's own billing, Zoho Billing Enterprise (₹24,999 a month)	₹2,99,988 a year	₹2,99,988 a year	₹2,99,988 a year
If Trendzo paid one Refrens business per retailer, Accounts Pro (₹15,000 a year)	₹15,00,000 a year	₹75,00,000 a year	₹3,00,00,000 a year

Reading the table:

Verification, GSTR-8 and TDS cost the same whether Trendzo has 100 or 2,000 retailers. A realistic platform-side compliance bill is roughly ₹36,000-61,000 a year before GST (GSTIN checks, a CA for GSTR-8 and the TDS return), and lower if the free GSTR-8 utility is used.
E-invoice minimums: on GSTZen's 18-paise plan you pay the ₹50,000 minimum until volume passes about 2.8 lakh invoices a year (50,000 ÷ 0.18); on the 50-paise plan the ₹25,000 minimum applies until 50,000 invoices a year (25,000 ÷ 0.50). Below those volumes the minimum, not the per-invoice rate, is the cost. Adaequare at 0.25 per IRN is ₹250 per 1,000 invoices, with no minimum shown.
E-way bill minimums apply per GSTIN, so 20 retailers on the 18-paise plan would cost ₹10,00,000 a year in minimums alone.
Paying for retailers' bookkeeping per retailer is the only line that scales linearly and gets very expensive. Do not offer it as a free feature.
The same applies to a billing product used for retailer invoices: one Refrens business per retailer at ₹15,000 a year, or one Zoho organisation per retailer, scales linearly with no platform discount. Trendzo's own commission billing is one account, so it does not grow with retailer count (Zoho Billing Enterprise adds 0.2% of monthly revenue above ₹2.5 crore).

In-house engineering and CA review time are not priced here because no public number exists. Add them from the team's own cost per developer-week in the next table.

7.3 Your shortlist (to be filled after the first review)

Placeholder. Add each shortlisted service and its quote below, and the comparison above will be extended to include them.

Service	Layer (verify, e-invoice, GSP, GSTR-8, TDS, CA)	Quoted price	Unit	Contract terms	Notes
(to add)
(to add)
(to add)

In-house cost inputs (to add): developer-week cost, estimated weeks per capability from section 4, ongoing maintenance weeks per year for rule changes, CA review fee.

8. Risks and open questions for a CA

Does Trendzo collect the shopper's money? The code says yes (Razorpay checkout). If yes, TCS, GSTR-8 and compulsory seller registration follow. If retailers collected directly, GST TCS would fall away but TDS would not.
SAC code for the commission. No official mapping exists; 998599 / 9985 is common practice, 9962 (retail on a fee basis) is arguable, software subscriptions may fall under 9973 or 9983.
Income-tax Act 2025 details. Payment code (secondary sources disagree between 1035 and 1037) and whether circulars issued under the 1961 Act carry over.
GST Council meeting on 7 Oct 2026. A single-state registration scheme for small sellers may change onboarding rules.
Unregistered enrolled sellers. What document they should issue, since they cannot charge GST.
Delivery fee and unregistered riders. Since 22 Sep 2025, local delivery by unregistered riders through an ECO is taxed under s.9(5) at 18%; check whether this affects Trendzo's riders.
Data protection. The DPDP Rules apply mostly from 13 May 2027 (a proposal to shorten the timeline is unconfirmed). Sole-proprietor GSTINs embed PAN and invoices carry shoppers' names, so they are personal data; GST and income-tax retention duties override erasure. Whether Trendzo is a data fiduciary or processor for retailers' invoice data is unclear.
Penalties. Failing to collect or deposit TCS, or letting an ineligible seller sell, can cost ₹10,000 or the tax involved, whichever is higher.
Prices not verified: Vayana, Swipe, Setu, Sandbox plans, India Compliance credits, TDSMAN, KDK, IndiaFilings, TaxBuddy, Razorpay Route, Cashfree Easy Split; the conflict between two WhiteBooks pages; Adaequare's currency symbol; GSTZen's GSP status; whether each GSTR-8 and TDS product has been updated for the new Forms 140 and 131.
Added after review (billing products): official prices for Zoho Billing Standard and Premium, Swipe, Vyapar and Cashfree; Refrens' page date, API fee, rate limits, webhooks and credit-note API; whether Refrens, Swipe or Zoho allow a partner to create businesses or organisations through the API and on what contract terms; Chargebee's India IRN details and which plan includes multi-entity; Zoho's per-plan GSTIN counts and e-way bill API. Whether a billing product's invoices count as the retailer's invoice (generated on its behalf) or Trendzo's needs a CA's view.

9. Recommended path

Phase 0: fix what exists (in-house)

Real platform GSTIN, series and place of supply on commission invoices; reverse commission on returns.
One TCS rate (0.5%) and one base, charged to retailers' payouts, not to shoppers.
Fix the month-close period format, lock closed periods, add retries for failed invoices.
Bill of supply for composition dealers online; capture buyer GSTIN for B2B.

Phase 1: close the platform's own filings

Seller-wise TCS and TDS ledgers; export a GSTR-8 CSV; file with the free offline utility or a CA.
TDS: produce Form 140 / 131 data; file with a managed service or a desktop tool.
Buy GSTIN verification (cheap API) at onboarding and on change requests.
Optional, for Trendzo's own commission and subscription invoices: evaluate Zoho Billing (or Books) against the in-house invoices once the defects are fixed. Do not use a billing product for retailer-to-shopper invoices.

Phase 2: help retailers file

Retailer GST pack (invoices, GSTR-1 and HSN data, TCS and TDS certificates) and a read-only CA role.

Phase 3: buy where it hurts

Only if retailers above ₹5 crore or large consignments appear: an e-invoice and e-way bill API on per-transaction pricing.
Only if filing on behalf of retailers becomes a product: a GSP with delegated credentials.

Decision gates: CA confirmation of section 8 items; number of retailers above ₹5 crore turnover; whether manual GSTR-8 and TDS filing takes more staff time than a managed service costs.

10. Sources

All read on 2026-10-03 unless stated.

Law and procedure

NACIN e-book on e-commerce operators and GST (Sept 2024): https://www.nacin.gov.in/ZCVisakhapatnam/Images/Documents/EBooks/e-Book%20on%20e-Commerce%20Operators%20and%20GST%20-%20NACIN%20Vizag%20(September,%202024).pdf
GSTR-8 FAQs, GST portal: https://tutorial.gst.gov.in/userguide/returns/FAQs_GSTR-8.htm
TCS rate cut to 0.5%: https://taxguru.in/goods-and-service-tax/cgst-e-commerce-operator-tcs-collection-rate-reduced-0-25-percent.html
GSTR-8 filing guide: https://cleartax.in/s/gstr-8-filing-guide-clear-gst
Enrolment facility for unregistered suppliers: https://www.taxscan.in/gstn-introduces-enrolment-facility-for-gst-unregistered-suppliers-to-supply-goods-through-e-commerce-operators-issues-advisory/331197
Local delivery under s.9(5) from 22 Sep 2025: https://blog.saginfotech.com/cbic-18-percent-gst-local-delivery-services-sept-22-2025
Composition dealers through ECOs: https://taxguru.in/goods-and-service-tax/gst-cbic-notifies-new-ecommerce-tax-rules-composition-taxpayers.html
Intermediary services circular: https://cbic-gst.gov.in/pdf/Circular-No-159-14-2021-GST.pdf
E-invoicing for ECOs and reporting limits: https://einvoice6.gst.gov.in/content/e-invoicing-for-e-commerce-operators/
E-invoice threshold: https://cleartax.in/s/e-invoicing-businesses-above-rs-5-crore-turnover
E-way bill Rule 138: https://gstlearn.com/2024/01/24/information-to-be-furnished-prior-to-commencement-of-movement-of-goods-and-generation-of-e-way-bill-cgst-rule-138/
Credit notes and IMS from 1 Oct 2025: https://taxguru.in/goods-and-service-tax/gst-amendments-finance-act-2025-effective-oct-1-2025-notified.html
Records and retention: https://gstgyaan.com/section-36-of-the-cgst-act-period-of-retention-of-accounts
TDS on e-commerce, 0.1% and s.393: https://blog.tdsman.com/2026/07/tds-on-e-commerce-transactions-section-3931-194o/ and https://taxgarden.in/blog/tds-on-ecommerce-payments-section-194o-393-guide-india-fy-2026-27
CBDT guidance on 194-O: https://www.bdo.in/en-gb/insights/alerts-updates/cbdt-issues-additional-guidelines-on-tds-by-e-commerce-operators-under-section-194-o-of-the-it-act
Form 140 / 131 FAQs: https://taxguru.in/income-tax/faqs-income-tax-form-140-quarterly-tds-return-non-salary-section-397-3-b.html
SAC for e-commerce commission: https://cleartax.in/s/gst-applicable-on-ecommerce-sale
Apparel rates from 22 Sep 2025: https://www.caclubindia.com/news/gst-rate-on-apparel-rationalised-18-percent-tax-for-garments-above-rs-2500-25945.asp
GST Council meeting 7 Oct 2026: https://www.startupadvisory.in/blog-57th-gst-council-meeting-12-september-2026.htm
DPDP timeline: https://www.pib.gov.in/PressNoteDetails.aspx?NoteId=156054&ModuleId=3&reg=3&lang=2

Vendors and prices

ClearTax: https://cleartax.in/s/e-invoicing-gst-compliance-solution/ · https://cleartax.in/tds
Adaequare: https://ugsp.adaequare.com/e-invoice-api · https://ugsp.adaequare.com/gst-apis
GSTZen: https://gstzen.in/e-invoicing-api-integration-pricing · https://gstzen.in/e-way-bill-api-integration-pricing-details · https://gstzen.in/gst-validator-api-pricing-details
WhiteBooks: https://whitebooks.in/about/pricing/ · https://whitebooks.in/api/gst-api-for-developers/
Sandbox.co.in: https://sandbox.co.in/pricing · https://sandbox.co.in/tds
Appyflow: https://appyflow.in/verify-gst/ · gstinapi: https://gstinapi.com/pricing · Eko: https://eps.eko.in/products/gst-verification-api
Masters India: https://www.mastersindia.co/e-invoicing-api/ · MasterGST: https://mastergst.com/gst/e-invoice-api.html
NIC and IRPs: https://einv-apisandbox.nic.in/onboarding.html · https://einvoice6.gst.gov.in/content/pricing-plan/ · https://einvoice3.gst.gov.in/introduction
Taxilla: https://www.taxilla.com/blog/gstr-8-filing
Gen GST and Gen e-TDS: https://saginfotech.com/PriceCalculator.aspx
Winman: https://www.winmansoftware.com/files/Software_pricelist_winman.pdf · KDK: https://www.kdksoftware.com/spectrum-cloud/tds/ · TDSMAN: https://www.tdsman.com/pricing.asp
Patron Accounting: https://www.patronaccounting.com/gst-returns-for-e-commerce-operator · EZTax: https://eztax.in/form26q-tds-return
Zoho Books: https://www.zoho.com/in/books/pricing/ · TallyPrime: https://tallysolutions.com/buy-tally/ · Cygnet Invoicing Tool: https://invoicingtool.cygnettaxtech.com/pricing/
Cashfree Easy Split: https://www.cashfree.com/docs/payments/split/billing/configuration · Razorpay Route: https://razorpay.com/route/ · Razorpay Invoices: https://razorpay.com/docs/api/payments/invoices/?preferred-country=IN
India Compliance: https://indiacompliance.app/
Added after review: Zoho Books API and e-way bill https://www.zoho.com/books/api/v3/introduction/ · https://www.zoho.com/in/books/help/e-way-bill/ · Zoho Billing https://www.zoho.com/in/billing/enterprise/pricing/ · https://goforfiling.com/zoho-billing-pricing/ · Zoho Invoice https://www.zoho.com/in/invoice/pricing/ · Zoho Commerce https://www.zoho.com/commerce/pricing/ · Refrens https://www.refrens.com/refrens-premium · https://www.refrens.com/api/docs/invoices/ · https://www.refrens.com/grow/reseller-invoice-api-aisensy-case-study/ · Chargebee https://www.chargebee.com/pricing/ · https://www.chargebee.com/docs/billing/2.0/taxes/indian-gst · https://www.chargebee.com/docs/billing/2.0/multi-business-entity/mbe-limitations · Swipe https://developers.getswipe.in/llms.txt · Vyapar https://www.softwaresuggest.com/vyapar · Razorpay https://razorpay.com/pricing/ · https://razorpay.com/docs/payments/route/ · Cashfree https://www.cashfree.com/docs/partners/embedded/commissions-and-invoices