Gst input for consumer

I am a cafe and juice bar owner. I am not registered under govt composition scheme of GST. Once a person came to our cafe and placed order and completed order. While paying the amount he asked my manager to include his GST number. As my software which is cafe management and billing software; have no such criteria to mention its GST NUMBER. He was saying he will get the input for such bills. Now my issue of discussion is that,what should we do in such cases. As per my knowledge he can claim tax paid expenses in his bill but not input. Kindly guide for the same