GST valuation rules on discounts, credit notes, and promotional schemes determine when discounts are excluded from supply value. Discounts given before or at the time of supply are excluded from the value of supply if recorded in the invoice, while post-supply discounts are excluded only when the statutory conditions are met, including issuance of a credit note and reversal of input tax credit attributable to the discount by the recipient. Promotional schemes such as free samples, buy-one-get-one-free offers, volume discounts, secondary discounts, No Claim Bonus, and incentive payments are addressed according to their treatment under the GST valuation rules.