Hello good evening sir, sir and need you help

sir mera ek client h us client ne may ko ek bill kata tha jiska invoice no. 010 aur yeh bill cash mai kata tha aur client ne cash ke bill ka tax le liya h...
but ek problem ho gyi ki mere client ko nahi pata tha ki ushe invoice vale bill ko Gst number per bhi kata rakha h may me 010 vale bill number ko lekin iska tax pay nahi kya h GST ka to ab iska kya solution h???


help me sir and please sir give solution? ??