Time of supply of services: tax liability arises at the earliest determinable event among invoice, payment, provision, or accounting entry. Time of supply of services is the earliest qualifying event among invoice issuance, receipt of payment, provision of service, or the recipient recording the receipt in its books. For reverse charge supplies the earlier of the recipient's payment entry or bank debit, or the date after a prescribed period following invoice issue, determines time of supply; if indeterminable the recipient's accounting entry controls. Vouchers are taxable on issue if identifiable or on redemption otherwise. Additions to value are taxable when received.