E-invoicing is the GST system where B2B invoices must be reported to a government Invoice Registration Portal (IRP), which returns a unique Invoice Reference Number (IRN) and signed QR code before the invoice is legally valid. As of Aug 2026 it is mandatory for every business whose turnover crossed ₹5 crore in any financial year since 2017-18.
Your billing software sends the invoice data to the IRP, which validates it, stamps an IRN and QR code, and sends it back — all in seconds when set up properly. The same data then auto-flows into your GSTR-1 and can generate the e-way bill, so a correctly configured system removes most manual return-preparation work. E-invoicing applies to B2B invoices, exports, and credit/debit notes, not to B2C sales.
The trigger is the part owners miss: crossing ₹5 crore in any year since 2017-18 — including a one-off good year in the past — puts you in scope permanently. If you're near the line, get your billing software IRP-ready before you cross it, not after. Most mainstream accounting packages handle it; the setup is a one-time exercise.
The costly mistake is issuing a plain invoice when you're in scope: without an IRN it is not a valid tax invoice, your buyer's input tax credit is at risk, and penalties apply per invoice. Also build a habit of checking supplier invoices — if a large supplier should be e-invoicing and isn't, their paper invoice is your ITC problem.
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Reviewed to the law in force in FY 2026-27. General information, not advice — confirm the position for your facts before acting.