Invoice Issuance for Continuous Supply of Services:
Under section 31(5)(a) of the CGST Act, where the due date of payment is ascertainable from the contract, the invoice must be issued on or before the due date of payment.
In this case, the due dates are clear from the Notice Inviting Applications and the FAL. Therefore, invoices must be issued on or before the due date of payment according to the option chosen by the telecom operator.