IGST refund process: GSTN-Customs invoice-level validation controls export tax refunds; correct returns or EGMs to resolve errors. Refund of IGST paid on exported goods is available to registered suppliers making zero-rated supplies either under bond/LUT by claiming unutilised input tax credit or by exporting on payment of IGST and claiming refund. The shipping bill is deemed the refund application once EGM and a valid GST return are filed. Automated refund processing matches GSTN return data with Customs shipping bill data at invoice level; validation errors (invalid SB details, EGM not filed, GSTIN mismatch, duplicate transmission, invalid invoice number, gateway EGM missing) must be corrected primarily via GST return amendments (Form 9A) or by contacting carriers/Customs, with PFMS bank validation and IEC status also affecting disbursal.