Reverse charge is applicable when there is a supply and the time of supply is
determined by section 12 or 13 of the CGST Act. Reverse charge is applicable at the time of advance even though actual supply is yet to take place. Rule 52 provides for the issuance of a Payment Voucher in cases where tax is to be paid on reverse charge basis.
(ICAI FAQ PUBLICATION 06-09-2017 REVERSE CHARGE: FAQ NO. 27)