To be fair I have almost the exact problem. For our next three cruises I had no problem booking both our first night suite dinners and our two included premier dinners on each cruise. The app showed that I had credits and did not charge me. However, the app just kept showing that I had credits even after I knew that I had used them all. So I booked a couple more dinners (that I am prepared to pay for), the app didn't charge me and confirmed the reservations. The app still show credits. I am not confident that Princess will catch this.