Transaction value determines taxable supply; specified inclusions and permissible discounts govern GST valuation and related party adjustments. Transaction value is the primary basis for taxable supply value where price is sole consideration between unrelated parties; value includes separately charged non-GST taxes and charges, amounts borne by recipient, incidental expenses, late payment charges, and subsidies linked to price. Discounts recorded on invoice or governed by pre-existing agreements (with reversal of attributable input tax credit) are excluded. Where transaction value cannot be applied, prescribed valuation methods or Government notified methods (on Council recommendation) determine value. Related persons and deemed relationships are defined for valuation adjustments.