No, we surprisingly do not want be reminded what our current balance is regardless of if we bought coins or not. It's just distracting and irrelevant.
So the mobile version of Webnovel added a bright orange sack of coins in the top right corner of your screen. Occasionally a coin will be dropped into the sack, which is just a pure animation. Your current balance would be listed next to the sack.
The problem is that the sack isn't on the main menu or even just hidden somewhere, but it's a part of the reading screen. Thus it will always be there until you realize that it is a part of the so called farming mode. This is a new mode that they added that was never really explained. I heard that you're supposed to receive ads that would then add coins to your balance, but I haven't noticed any yet.
So yeah, just disable farming mode to make the bag disappear.