I am constructing a building for my client. The client is required to pay me on completion of plinth, 1st floor and 2nd floor. When should the invoice be raised?

The above instance is a case of continuous supply of services. Here, since the payment is linked to completion of an event (i.e., milestones set in the contract), an invoice should be raised on or before the due date of completion of event as per section 31(5)(c) of the CGST Act, 2017. Therefore, an invoice be raised on or before completion of the 1st floor and the second time on or before the completion of 2nd floor.

(ICAI FAQ PUBLICATION 06-09-2017 -: Tax Invoice, Credit and Debit Notes : FAQ NO. 10)