IRN
IRN is the short name used for the FBR invoice number: the unique number issued by FBR's Digital Invoicing system when an invoice passes validation and is accepted. It is proof that the invoice was transmitted to FBR. The number, together with a QR code generated from it, must be printed on the invoice given to the buyer. The number cannot be changed afterwards; corrections are made on IRIS under FBR's 72-hour rule.