Post-sales discounts under GST: characterisation determines whether they reduce supplier value or constitute taxable separate supplies. Post-sales discounts under clause (b) of section 15(3) CGST are to be characterised by their commercial nature: discounts without further dealer obligations relate to the original supply and may be excluded from the supplier's value of supply; discounts that require the dealer to perform promotional activities are separate supplies of services on which the dealer must charge GST and the supplier may claim ITC; discounts paid to induce dealers to lower customer prices must be added to the dealer's consideration for valuation. Where discounts cannot be excluded, suppliers may issue financial/commercial credit notes but cannot reduce original tax liability, and dealers need not reverse ITC if they pay the reduced value after adjusting such credit notes in line with applicable provisos.