Time of supply of goods determines tax liability based on earlier of invoice or payment, with special procedural rules. Time of supply of goods is the earlier of invoice issue (or last date for issuing it) and receipt of payment, where receipt is the earlier of entry in books or bank credit; a limited excess receipt may be optionally treated as at invoice date. For reverse charge supplies the earliest of receipt of goods, payment as recorded or bank debit, or the date after the prescribed period from invoice applies, with fallback to recipient's books if indeterminable. Vouchers are timed to issue or redemption, fallback to return filing or payment applies, and additions to value are timed to supplier receipt.