My bad on paid in full, wasn't too sure.
I did have this exact issue with the app. I previously made a reservation for Sabatini's through the app no problem. I later tried it for Sterling Steakhouse and it wanted to charge me. Others suggested to use the web version of the app to make reservations. I decided to give it a try that and it worked no problem. So it might not hurt for OP to try as well. Much easier than trying to get refunded while on board.