Invoice Reference Number requirement: upload invoice particulars in FORM GST INV-01 to validate invoices within the prescribed timeframe. Registered persons who prepared tax invoices otherwise than as prescribed must, for invoices issued in the specified period, obtain an Invoice Reference Number (IRN) by uploading prescribed particulars in FORM GST INV-01 on the Common GST Electronic Portal within thirty days from the invoice date; failure to obtain the IRN within that period will result in the document not being treated as an invoice.