The Invoice Reference Number (IRN) is unique (also known as hash) generated by the e-invoice system using a hash generation algorithm.
For every document viz., an invoice or debit or credit note to be submitted on the e-invoice system, a unique 64-character Invoice Reference Number (IRN) shall be generated, which is based on the computation of hash of GSTIN of supplier of a document (invoice or credit note etc.), Year, Document type and Document number.
This shall be unique to each Invoice and hence will be the unique identifier for each Invoice for the entire financial year in the entire GST System for a taxpayer.