Rate of exchange determination revised for taxable supplies, using Customs rates for goods and GAAP for services. Amendments revise deadlines and procedures: Rule 24's deadline substituted to on or before 30th September 2017 (deemed from 22nd July 2017); Rule 34 prescribes exchange-rate methods-Customs-notified rate for goods and GAAP-determined rate for services at time of supply; absent input invoices, values are estimated at prevailing market price; export/SEZ invoice endorsements must state export/SEZ supply status and include recipient, delivery address and country; Rule 61 permits FORM GSTR-3B filing when GSTR-1/GSTR-2 are extended and prescribes electronic generation, reconciliation and credit ledger adjustments for FORM GSTR-3.