Change in rate of tax determines time of supply, prioritising earlier of invoice issue or payment receipt after rate shifts. Change in rate of tax determines the time of supply by prioritising invoice date or date of receipt of payment depending on whether supplies fall before or after the rate change. For supplies before the change, the earlier of invoice issuance or payment receipt governs unless one occurred before and the other after the change, in which case the event occurring before the change governs. For supplies after the change, analogous prioritisation applies. Receipt of payment is the earlier of book entry or bank credit, with bank credit treated specially when delayed beyond a working-day threshold.