I’VE JUST SOLVED THIS FOR MY CARD. My mastercard expired and was renewed. The card didn’t automatically update in Apple Wallet and I had a notification to add new card details. When I tried (felt like several hundred times 😂) I had the “cannot add card” message. I spent the entire morning trying to sort it, reading posts like these with no luck. The I spoke to my card provider’s digital wallet team (who knew there was such a thing?) who solved it within 5 minutes. The problem (in my case) was that there were too many “devices” linked to my card so when I tried to put it onto Apple Wallet it was bounced. Turns out “devices” aren’t physical devices like phones and ipads but are “tokens” which are used by retailers when you input your card details and they make a request to the card provoder to keep your card details. Not every retailer you make transactions with counts as a “token” and there is no way of knowing which do and which don’t. My tokens included Amazon, Ocado, Trainline, Uber, Netflix but not Spotify, Waitrose, TfL so there’s no logic to it. You are only permitted 9 tokens in total and Apple Pay is one of them. The digital wallet team at my bank went through all my tokens with me and deleted those I no longer need. Now my mastercard is in my Apple Wallet 🥳. So if you have the same problem (clue is that other cards are accepted) try calling your bank’s digital wallet team and ask them to look at “tokens”. It worked for me - hope it works for you too. I only spent a few hours trying to sort it but nearly lost the will to live.