Time of supply of vouchers: single-purpose tied to issue, multi-purpose tied to redemption under GST, affecting invoice timing. Time of supply for vouchers depends on whether the voucher is a single-purpose voucher (time of supply is date of issue) or a multi-purpose voucher (time of supply is date of redemption). Invoice-timing rules require issuance before or at removal or delivery, affecting when tax is chargeable for voucher transactions. Regulatory treatment of prepaid payment instruments as closed, semi-closed or open PPIs influences whether an instrument functions like money or a redeemable voucher for GST purposes.