Trouble Using Apple Pay for In-App Purchases

I'm having trouble using Apple Pay on my iPhone 16. I want to buy the Pass Royale in Clash Royale, but every time I try, I get a message saying, 'your payment method was declined. Tap continue to change your payment information, if you cancel, you may not be able to buy until this billing issue has been resolved.' I've checked and have enough funds, and my Apple Pay information is all updated with the correct address and details. This issue has never happened before, so I'm looking for advice on what to do next.