What Is GST E-Invoicing and the IRN? A Plain Guide

Without e-invoicing, you raise an invoice, send it to the customer and report it later in your returns. With e-invoicing, there is an extra step between raising the invoice and treating it as final. The invoice data goes to an IRP for registration, and the invoice carries the IRN and QR code that the IRP returns.

Your invoice format, numbering series and accounting entries remain your responsibility. E-invoicing standardises how invoice data is reported and authenticated. It does not replace your books, your invoice checks or your review of returns before filing.

The documents covered are invoices, credit notes and debit notes issued by notified businesses, for supplies to registered buyers and for certain other supplies such as exports and supplies to special economic zones. Only credit and debit notes issued under the GST law are reported, not purely commercial ones. The exact scope and exclusions are set by notification, so check the current position before you configure your software.

Think of the process as a loop: your system sends data out, receives a registration back, and the GST system uses the same data for returns. The flow below shows each step in order.

1. Create the invoice in your billing or accounting software, with the customer GSTIN, place of supply, item details, HSN or SAC codes, taxable value and tax amounts.
2. Your software converts the invoice into the prescribed e-invoice schema, usually as a JSON file.
3. The JSON is uploaded to an IRP, either directly through an integration, through a service provider, or by preparing and uploading the file manually.
4. The IRP validates the data, including the GSTIN details and the uniqueness of the supplier GSTIN, document type, document number and financial year combination.
5. If validation passes, the IRP generates the IRN and returns the signed invoice data and a signed QR code. If it fails, the IRP returns an error and no IRN is issued.
6. Your software stores the IRN, acknowledgement details and QR code against the invoice, and prints the QR code on the invoice copy sent to the customer.
7. The IRP shares the registered invoice data with the GST system, where it can populate the relevant tables of your outward supply return and appear in your customer's auto-drafted input tax credit statement.
8. Before filing, you review the auto-populated return data against your sales register and correct any gaps or mismatches.

Where an e-way bill is also needed, the e-invoice data can support its generation if transport details are supplied. Confirm the current e-way bill requirements separately, as they follow their own rules.

The IRN is a unique reference generated by the IRP for each registered document. It is a 64-character hash based on the supplier GSTIN, the document type, the document number and the financial year. Because of this, the same invoice number cannot be registered twice by the same supplier for the same document type and year.

The signed QR code carries key invoice details, such as the supplier and recipient GSTINs, the invoice number and date, the invoice value, the number of line items, the main HSN code and the IRN with its generation date. A customer or officer can scan it to check that the invoice was registered, without needing to log in to the GST portal.

Most problems with e-invoicing come from master data and settings, not from the portal. Run through this checklist with your software provider before the first live invoice, and test it in a sandbox or test environment if one is available.

• ✓Your own GSTIN, legal name, trade name and addresses match the GST registration, including any additional places of business.
• ✓Customer master records hold verified GSTINs, correct state codes and the right registration type for each party.
• ✓Every item and service has a valid HSN or SAC code and the correct unit of measure.
• ✓Place of supply logic correctly decides between IGST and CGST plus SGST for each type of transaction.
• ✓Invoice numbering series follow the prescribed format and length, are unique within the financial year and never reused after a cancellation.
• ✓Credit notes and debit notes reference the original invoice and are configured as separate document types.
• ✓API credentials or IRP access are set up for the right GSTIN, and access is limited to authorised users.
• ✓The software stores the IRN, acknowledgement number, acknowledgement date and QR code against each invoice and prints the QR code on the customer copy.
• ✓Errors returned by the IRP are shown clearly to the user, and invoices that failed registration are blocked from being sent as final.
• ✓There is a documented fallback for portal downtime, such as holding invoices and registering them once the service resumes.
• ✓A cancellation process exists for IRNs within the permitted window, with a matching credit note process after that window.
• ✓A test run has been done for each document type and each tax pattern you use, and the outputs have been reviewed by your finance lead or CA.

The GST invoice checklist for service businesses covers the invoice content checks that should already be in place before you add e-invoicing on top.

An IRN cannot be edited. If the invoice is wrong, you have two broad routes. Within the cancellation window allowed by the IRP, you can cancel the IRN in full; partial cancellation is not possible. After that window, or where the invoice has already been reflected in a filed return, corrections are generally made through a credit note or debit note, which is itself reported to the IRP where e-invoicing applies. Confirm the current cancellation window and rules on the GST portal or with your CA.

Once an IRN is cancelled, the same invoice number cannot be used to register another e-invoice, so issue the corrected invoice under a new number. Where the error is the customer GSTIN, the guide on correcting an invoice with the wrong customer GSTIN walks through the options step by step.

• Sending the customer a PDF invoice before the IRN has been generated.
• Assuming the auto-populated return is correct without reconciling it with your sales register.
• Reusing an invoice number after cancelling its IRN.
• Leaving customer GSTINs unverified in the master, which leads to rejections or wrong credit for the customer.
• Treating a portal error as a software fault and bypassing it rather than fixing the underlying data.
• Registering documents under the wrong GSTIN where a business holds more than one registration.
• Forgetting to register credit notes and debit notes that fall within the scheme.

This guide does not cover who must adopt e-invoicing or from when, and it does not cover export, special economic zone or other specialised supplies in detail. Check the current applicability rules on the GST portal or with your CA, and confirm any supply type you are unsure about before switching it on in your software.