Retention payments: no GST if supply occurred before transition and tax was already paid under the earlier law. Where goods or services were supplied before the appointed day but part of the consideration is received on or after the appointed day, no tax shall be payable under the new law if the full duty or tax on that supply has already been paid under the earlier law; this rule applies notwithstanding sections on chargeability and is reflected in both central and state GST enactments.