Consideration for supply determines GST: compensatory payments are non taxable unless they constitute consideration for a contractual supply. GST liability depends on whether a payment is consideration for a supply under the declared service of agreeing to refrain from, tolerate, or do an act. That service requires an express or implied agreement and reciprocal consideration; absent such contractual arrangement, compensatory payments arising from breach, statutory cancellations, penalties, cheque dishonour fines or forfeitures are mere flows of money and not taxable. Conversely, contractual charges that constitute ancillary or independently bargained facilities (late payment acceptance, cancellation fees, prepayment penalties) are consideration for supply and taxable alongside the principal supply unless the principal supply is exempt.