Invoice Reference Number requirement: registered persons must obtain IRN via FORM GST INV 01 within thirty days or invoice not recognised. Notification requires certain registered persons, during the stated period, to obtain an Invoice Reference Number (IRN) by uploading prescribed particulars in FORM GST INV-01 on the Common GST Electronic Portal. The IRN must be obtained within thirty days from the date of the invoice; failure to do so means the invoice shall not be treated as an invoice.