Time of supply of goods determines GST liability based on invoice issuance or earlier receipt of payment, shaping tax timing. The provision fixes the time of supply for goods as the earlier of invoice issuance (or required last issuance date) and receipt of payment, with supply limited to the extent covered by invoice or payment and payment treated as received when entered in books or credited to bank. For reverse charge supplies the earliest of receipt of goods, payment recorded or bank debit, or expiry of a statutory period from invoice governs; vouchers are timed at issue if identifiable or at redemption. Residual rules use return filing date or tax payment date, and additions like interest and late fees are timed to receipt by the supplier.