Section 142(2)(a) in The Punjab Goods and Services Tax Act, 2017
(a)where, in pursuance of a contract entered into prior to the appointed day, the price of any goods is revised upwards on or after the appointed day, the registered person who had sold such goods shall issue to the recipient a supplementary invoice or debit note, containing such particulars as may be prescribed, within thirty days of such price revision and for the purposes of this Act, such supplementary invoice or debit note shall be deemed to have been issued in respect of an outward supply made under this Act;