Sounds like you restored a backup from iCloud.
I’ve just gone through (minor) hell with the same issue on a Pixel 8 and Google Wallet with Monzo cards - after choosing to transfer stuff across from the old phone rather than starting from scratch. 24 hours later (following a 40 minute chat with Monzo and a 1 hour 30 min (
) chat with the Google Pay team which proved totally wasted) - I did a factory reset and started from scratch. Lo and behold - no issue adding Monzo cards to GWallet.
So if you transfer data (either from an existing phone or from an iCloud backup) - you’re likely to hit issues. My recommendation - start from scratch after a factory reset and add things manually.
There’s a few pointers here too: