Exchange rate determination clarified for goods and services; export invoice endorsements and GSTR-3B filing procedures specified under GST rules. The amendment sets exchange-rate rules for valuation-Customs-notified rates for goods and generally accepted accounting principle rates for services-and revises export invoice endorsements and return-filing mechanics: export invoices must carry specified endorsements and recipient/delivery/country details; the Commissioner may require FORM GSTR-3B where GSTR-1/GSTR-2 timelines are extended and electronic generation, reconciliation and crediting procedures between GSTR-3, GSTR-3B and GSTR-2 are prescribed.