Time of supply rules determine tax point when GST rate changes, prioritising earlier of invoice or payment. Change in rate of tax alters the time of supply, fixing the tax point by the relative timing of invoice issuance and payment receipt: for supplies before the rate change, the earlier of invoice or payment governs when both occur after the change; invoice governs if issued before while payment after; payment governs if received before and invoice after. For supplies after the change, payment governs if received after but invoice prior; the earlier of invoice or payment governs if both precede the change; invoice governs if issued after but payment before. Bank credit beyond four working days fixes payment to the bank credit date. 'Date of receipt of payment' is the earlier of book entry or bank credit.