Time of supply of goods determines tax liability based on invoice date, payment receipt, or specified reverse charge and voucher rules. Time of supply for goods is the earlier of invoice issuance (or last permitted invoice date) and receipt of payment, with payment deemed when entered in books or credited to bank. For reverse charge supplies the earliest of receipt of goods, payment recorded or debited in recipient's accounts, or the date after thirty days from supplier's invoice applies, with book entry as fallback. Vouchers use issue date if identifiable otherwise redemption date. If none apply, the filing date of periodic returns or the date of tax payment determines time. Additions like interest or late fees are taxable when received by the supplier.