Invoice Reference Number requirement mandates uploading invoice particulars on the GST portal or the invoice will not be recognised. Notification requires registered persons who prepared tax invoices otherwise than as specified to obtain an Invoice Reference Number (IRN) by uploading specified particulars in FORM GST INV-01 on the GST Electronic Portal for invoices issued between 1 October 2020 and 31 October 2020, and to do so within thirty days from the invoice date; failure to obtain the IRN within that period means the document will not be treated as an invoice.