Value of supply: transaction value principle defines taxable value and mandated inclusions and exclusions. Value of supply is the transaction value where supplier and recipient are not related and price is sole consideration; value must include certain taxes and charges (other than specified GST Acts) when separately charged, amounts paid by recipient on supplier's behalf, incidental expenses (commission, packing), interest or penalties for delayed payment, and subsidies directly linked to price received by the supplier; discounts are excluded if invoiced at or before supply or if post-supply discounts meet agreement and input tax credit reversal conditions.