Apple Pay isn’t working online but works in person

My card is added to my Apple wallet, and it works in stores in person, when I tap it on the card reader it works fine. But when I try to make online purchases using Apple Pay it asks me to add my card (even though it’s already added to my wallet) so I enter my card details and it says “card already added to wallet”, yes I know it’s already added so why won’t it let me pay? And so I pressed the only button there is which says “add card later” and the cycle starts again. I’ve tried deleting and re-adding my card to my Apple wallet, signing in and out of my Apple ID, but nothing seems to work. I don’t think anything is wrong with my card because it works in person? I don’t know. Any advice would be helpful.