Advance amount received on services

sir. my client is a contractor for provision of service. He receives advance and lator on after completion of work he will raise the invoice. now when i receive advance , i have to discharge the GST and the same is to be reported in GSTR 1 under advance received tab and when we raise the invoice, then we will make adjustment - right.
but the customer wants the GST credit at the time of advance only, how it is possible?.