B2B Catalogue Marketplaces: GST E-Invoicing as a First-Class Feature

The discovery-to-IRN-generation arc

A B2B marketplace transaction is not over when a buyer places an order — it is over when the GST portal issues an Invoice Reference Number against that order. The marketplaces that treat these as the same event (catalogue search → order confirmation → IRN generation as one continuous flow) eliminate an entire class of month-end firefights. The marketplaces that treat them as separate events — order on day one, manual invoicing on day five — produce the chaos that Indian B2B finance teams have endured for two decades.

HSN codes at the catalogue layer, not at billing

The most common e-invoicing failure on B2B marketplaces is the wrong HSN code on a line item. This happens because HSN is typed at billing time by someone who is not the product expert. The fix is structural: HSN codes belong at the catalogue layer, captured at product-master setup, validated against the official GST HSN list, and locked from edit at the line-item level. A marketplace that enforces this single rule reduces e-invoice rejections by 60-80% within one billing cycle.

• HSN code captured at product-master setup, validated against the official GST list
• Tax rate auto-derived from HSN — never typed per invoice
• HSN locked from edit at the order-line-item level (only product master can change it)
• HSN audit log for any product-master HSN change (with finance approval)
• HSN-change effective-date controls so historic orders keep their original code

Place of supply: state code, not free text

Place of supply determines whether a B2B transaction is CGST+SGST (intra-state) or IGST (inter-state). The GST portal validates this against the buyer's GSTIN state code — not against the marketplace's free-text shipping address. The marketplace must derive place of supply from the GSTIN itself (the first two digits of GSTIN are the state code) and apply the resulting tax structure automatically. Buyers who later challenge tax treatment can always point to the GSTIN as the source of truth.

What to do when the GST portal rejects an IRN

Even with HSN and place-of-supply discipline, some IRN generations will fail — portal downtime, GSTIN status changes, or value mismatches. The marketplaces that handle this gracefully follow a four-step recovery: capture the rejection reason verbatim in the audit log, surface the failure on the seller dashboard (not just the accounting backend), auto-retry within the 24-hour IRN cancellation window if the reason was transient, and escalate to seller-side finance if the reason was structural. Marketplaces that swallow rejection silently create month-end reconciliation hell.

Designing for the buyer's accountant, not the buyer

The single most under-served user of B2B catalogue marketplaces in India is the buyer's accountant — the person who reconciles invoices, files GSTR-2B credits, and chases sellers when a credit does not appear in the right month. Marketplaces that design for the accountant — bulk invoice download in GST-compliant format, IRN status visible on every order, monthly reconciliation reports, credit-note workflow built in — win the procurement-side recommendation that drives long-term volume. The buyer signs the order; the accountant recommends the marketplace at next year's review.

A B2B marketplace that cannot generate a valid IRN within 60 seconds of order placement is a catalogue, not a marketplace.

Internal B2B marketplace audit, 2024