Suppose u collect 100000 plus 18% gst from airtel and give 80000 to different vendors
Your output gst is 18000
Inout gst is 0(as vendors are unregistered)
Gst payable =18000-0=18000
Note
Pur from registered dealer was covered under reverse charge.. Now it is suspended from 13 Oct 2017 so no tax payable on payment to unregistered vendors