We have a substantial amount of on board credit for a P&O Cruise next March (2023). Our experience is that if you leave booking an excursion until you are on board then many are fully booked. We would like to use that credit against a number of excursions, BUT only if it is paid for with the onboard credit. (i.e. we do not want to have to pay with our own 'hard earned cash' 😁). My question is that if I book an excursion now (i.e. before I am on board) will that mean that I have to pay in full now/when our balance is due and not be able to use my onboard credit to pay for that excursion?