Refund under GST: electronic filing, evidentiary proof, and formulaic calculation for zero rated and inverted duty credits. Refund claims under GST must be filed electronically in FORM GST RFD-01 except where alternate filing is specified; export and SEZ-related claims have specific timing and endorsement prerequisites. Claims require documentary evidence tailored to the refund category, declarations or accountant certificates regarding non passage of tax incidence depending on claim value, and debit of the electronic credit ledger where refund relates to input tax credit. Refunds for zero rated supplies under bond/LOU and for inverted duty structure are calculable by prescribed formulae using Net ITC, turnover of relevant supplies and Adjusted Total Turnover.