Section 14(a) in The Punjab Goods and Services Tax Act, 2017
(a)in case the goods or services or both have been supplied before the change in rate of tax,-(i)where the invoice for the same has been issued and the payment is also received after the change in rate of tax, the time of supply shall be the date of receipt of payment or the date of issue of invoice, whichever is earlier; or(ii)where the invoice has been issued prior to the change in rate of tax but payment is received after the change in rate of tax, the time of supply shall be the date of issue of invoice; or(iii)where the payment has been received before the change in rate of tax, but the invoice for the same is issued after the change in rate of tax, the time of supply shall be the date of receipt of payment;
