Time of supply of vouchers determines tax point: issue date for identifiable vouchers, redemption date for non identifiable vouchers. Section 13(4) addressed the time of supply for vouchers exchangeable for services: where the underlying supply is identifiable at issue (single purpose voucher) the tax point is the voucher issue date; where it is not identifiable (multi purpose/general purpose voucher) the tax point is the redemption date. This rule is considered alongside invoice timing provisions of section 31 for services. The summary also contrasts the VAT directive definitions and explains RBI regulation of prepaid payment instruments (closed, semi closed and open PPIs) and their authorisation and operational limits.