Change in rate of tax alters time of supply rules; invoice and payment timing determine the applicable tax rate. Change in rate of tax determines the time of supply by reference to the timing of supply, invoice issuance and receipt of payment. If supply occurs before the rate change, the time of supply is the earlier of invoice date or payment date when both fall after the change; invoice date governs where invoice precedes but payment follows the change; payment date governs where payment precedes but invoice follows. Where supply occurs after the change, the sequencing of invoice and payment similarly fixes the time of supply, and 'date of receipt of payment' means the earlier of book entry or bank credit.