IGST refund procedure: exporters to submit CA certificates or proof of IGST payment to enable transmission and sanction. Sanction of pending IGST refund claims where GSTN transmission to Customs EDI was blocked is enabled through a two track procedure: for no short payment, Customs will identify exporters with matching cumulative IGST in GSTR 3B and GSTR 1 and process refunds upon receipt of a Chartered Accountant certificate to the port customs and jurisdictional GST office; for short payments, exporters must pay the shortfall, submit proof of payment (and a CA certificate for larger claims), provide an undertaking to repay if necessary, and be listed for GSTN transmission and post refund audit.