Time of supply of services :
The liability to pay CGST/SGST on services shall arise at the time of supply as determined in terms of the provisions of section 13 – section 13(1) of CGST Act.
As per section 13(2) of CGST Act, the time of supply of services shall be the earliest of the following dates, namely:—
(a) the date of issue of invoice by the supplier, if the invoice is issued within the period prescribed under section 31(2) of CGST Act or the date of receipt of payment, whichever is earlier; or
(b) the date of provision of service, if the invoice is not issued within the period prescribed under section 31(2) or the date of receipt of payment, whichever is earlier; or
(c) the date on which the recipient shows the receipt of services in his books of account, in a case where the provisions of clause (a) or clause (b) do not apply.
Explanation .—For the purposes of clauses (a) and (b) (i) the supply shall be deemed to have been made to the extent it is covered by the invoice or, as the case may be, the payment (ii) “the date of receipt of payment” shall be the date on which the payment is entered in the books of account of the supplier or the date on which the payment is credited to his bank account, whichever is earlier.
GST if advance upto Rs 1,000 received can be paid at the time of issue of invoice – Where the supplier of taxable services receives an amount up to one thousand rupees in excess of the amount indicated in the tax invoice, the time of supply to the extent of such excess shall, at the option of the said supplier, be the date of issue of invoice relating to such excess payment – proviso to section 13(2) of CGST Act.
Thus, if advance upto Rs 1,000 is received, GST is not payable at that stage. In that case, GST will be payable when invoice is raised.