As for me, this app has solved the main task – I am not reminding my students of payments, the app automatically does this for me)). Previously I had to remind the most "forgetful" students of a debt and I was always feeling uncomfortable doing that.
Once the app sends a reminder, the students recall of the debt and pay for the sessions. It is easy to add new clients, to see the payments received as well as the debt. People on a sick leave may be paused and then be back into the sessions with either postponing the sessions or adjusting the amount.