As far i seen we are paying GST only for transaction charge took by exchanges like 1% transaction charge + 18% transaction charge for that fee . Lets say 10000 rs transaction you have to pay 100 rs fee + 18% of 100 rs = 118 rs So for the transaction 10000 you have t pay 10118 rs.
Perfectly explained. As for Unocoin I am not sure how they are paying taxes only on fees, as they are literally providing bitcoin as commodity and not a service of co-ordinating between two traders.