Re: Apple Pay: "Payment it’s been doing this and I’m not sure how to fix it"
Seems when you add a card to Wallet to use for Apple Pay,
the card needs to be verified by your card-provider, who approves it for use with Apple Pay..
See Apple Support's article: Set up Apple Pay - Apple Support
NB: Step 4 of "How to add a debit or credit card on your iPhone" in the article above
says:
"Verify your information with your bank or card issuer.
They might ask you to provide more information
or
to download an app before approving your card for use with Apple Pay."