Hi!
I am new here. I am not sure if this is a common problem but I found more than once that tapping on the pay button on the shared tab is all too easy. I’ve tapped that button by mistake a few times and repaid full amounts I owed right before I could entirely by mistake.
You may want to look at adding an extra step asking you “are you sure you want to pay in full?” And even giving the possibility to pay a certain amount and not the amount in full at all times.