Supervision charges on exampted goods.

Sir,

I have a company and I am doing supervision service to other warehouse.
Now I am supervise exampted goods ( Rice) in warehouse. Problem is that what is the Gst impact. I am giving Gst bill to the party but party saying that materials is exempted the bill will be no gst.
Please suggest what is the actual rules and what is the notification.

Thanks in advance
Regards
Avishek Mukherjee