GST e-invoicing guide for 2026

By the QuantProc team · Updated 21 October 2026

What is a GST e-invoice?

An e-invoice is a normal GST tax invoice that is reported to the government's Invoice Registration Portal (IRP) in a standard format. The IRP checks it, assigns a unique Invoice Reference Number (IRN), signs it and returns a QR code that must be printed on the invoice. The details then flow automatically to the GST system for returns and to e-way bills.

Who must generate e-invoices?

E-invoicing applies to a registered business whose aggregate annual turnover crossed ₹5 crore in any financial year from 2017-18 onwards. Once you have crossed the limit in any year, the requirement continues even if turnover later falls.

It covers B2B supplies, exports and supplies to SEZs, along with the credit and debit notes against them. Certain sectors are exempt, including banks and other notified financial institutions, insurers, goods transport agencies, passenger transport, and cinema admission services. SEZ units themselves are also exempt.

The 30-day reporting rule

Businesses with aggregate turnover of ₹10 crore or more must report each invoice, credit note and debit note to the IRP within 30 days of the document date. After that the IRP rejects it, and an invoice without a valid IRN is not a valid tax invoice, so the buyer cannot claim input tax credit on it. For businesses between ₹5 crore and ₹10 crore the portal does not yet enforce the 30-day block, but reporting immediately is still the safe practice.

How the process works

1. Your billing or ERP system creates the invoice in the e-invoice schema.
2. It sends the invoice to the IRP, directly or through a GST Suvidha Provider.
3. The IRP validates it, generates the IRN and returns the signed invoice with the QR code.
4. You print or send the invoice with the QR code to the buyer.
5. The data moves to GSTR-1 automatically, and an e-way bill can be generated from it.

Common mistakes

• Wrong GSTIN or state code of the buyer. The IRP rejects it; validate GSTINs before billing.
• Missing or short HSN codes. At least 4 digits are required up to ₹5 crore turnover and 6 digits above it.
• Reporting late. With the 30-day limit, an invoice made on the 1st and forgotten until next month can be lost.
• Cancelling instead of issuing a credit note. An IRN can be cancelled only within 24 hours; after that, issue a credit note.
• Two systems. Making invoices in one tool and uploading them by hand to another invites errors.

Doing it without extra work

The simplest way to stay compliant is to generate the e-invoice from the same system that makes the invoice and keeps the books. In QuantProc billing, the IRN and QR code are fetched as you save a B2B invoice, and the invoice posts to accounts at the same time. For one-off invoices below the e-invoice limit, use the free GST invoice generator.