Time of supply determines tax liability: invoice or payment timing governs, with special rules for reverse charge and vouchers.

Tax liability on goods arises at the time of supply, ordinarily the earlier of invoice issuance (or the last required invoice date) and receipt of payment, with payment treated as the earlier of book entry or bank credit. For reverse charge supplies the earliest of goods receipt, recipient's payment entry or bank debit, or a specified post-invoice period applies, with recipient's books as fallback. Voucher supplies are timed at issue if identifiable, otherwise on redemption. Where none apply, the return filing date or tax payment date determines time of supply; additions like interest are timed to receipt.

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