Invoice for FY 19-20 & Submit in Fy 20-21

Dear Sir,
We received services from a chennai based co. & place of service is west bengal in the month of January 2020 and we advanced them half the amount. After completing the job we requested them to submit the bill. But, they submitted the bill in July 2020. Now henceforth how do we post the bill for GST return.
Regards,