GST per digital transaction

Hello Sir/Madam,
Considering a application where user loads in money through payment gateway and after sometime that user gets back that money (same or increased/decreased amount) as winning money through some payout system. This process continues

I wish to know :
1) If & how much gst is applicable for every load in money of such users.
2) If any gst is applicable to return the money as winning money to users.
3) If any other taxes applicable for such transaction.

Thanks