Refund of IGST on zero rated supplies requires shipping bill or formal refund filing and Customs or tax authority processing. Refunds of IGST on zero rated supplies permit two routes: export under bond/Letter of Undertaking to claim unutilised input tax credit, or export on payment of IGST and claim refund of tax paid. For goods exports the shipping bill together with a valid GSTR-1 and GSTR-3B/GSTR-3 filing constitutes the refund claim under Rule 96 and Customs processes and disburses the refund after electronic validation. Service exporters and suppliers to SEZs must file FORM GST RFD-01 (or RFD-01A for manual claims) with prescribed invoice statements and SEZ endorsement evidence for refund processing.