Time of supply of goods: earliest of invoice issuance or payment receipt; distinct rules govern reverse charge and vouchers. Liability to pay tax on goods arises at the time of supply, which for standard supplies is the earlier of invoice issuance (or last permitted invoice date) and receipt of payment; payment is the date entered in books or bank credit, whichever is earlier. For reverse charge supplies the time is the earliest of receipt of goods, payment recorded/ debited by recipient, or the day after thirty days from supplier's invoice, with fallback to the recipient's book entry if necessary. Voucher supplies and additions to value (interest, late fees, penalties) have their own time-of-supply rules.