GST is not applicable to my customer other company's account dept. force to get GST number from him.

One of my customer have section 8 company working as charitable foundation, another company dealing with them is pvt ltd. The foundation have given Rs.56000 to pvt ltd company for event preparation. To make invoice pvt ltd company demanding GST number from him while he is not applicable to GST because his turnover is just 2 lakh rs. What should I suggest him to do?