The Invoice Reference Number (IRN) is a 64-digit along alphanumeric number to uniquely identify each B2B Invoice issued in India. The IRN is calculated from the following details:
by concatenating the details together and computing a SHA 256 hash.
For example, the IRN for the following invoice details
will be SHA265("29AAFCC9980M1ZR2019-20INV2019-20/KA/1") which is 23f498ee41441ecad30f72ba5b9907506c3df70a17b0e0dff46b76a786400662.
Any supplier using their accounting software can generate an IRN against each invoice. In fact a user could print a bill book (though that would go against the whole concept of e-Invoice) of serially running invoices with unique IRNs. However, the Invoice and IRN alone are not valid.
As per CGST Rule 48(4) - Manner of Issuing Invoice and CGST Notification 70/2019, tax payers with aggregate turnover in a financial year more than Rs. 100 Crore are required to generate an e-Invoice, register it with a Government-approved Invoice Registration Portal (IRP), receive an Invoice Reference Number (IRN).
To help a recipient or buyer validate that their supplier has registered their invoice with the Invoice Registration Portal (IRP), the IRP will issue a digitally signed invoice and Quick Response Code (QR Code). The supplier can print the QR Code on their invoice or directly share the digitally signed invoice with their customer.