It has been working fine for me, and don't see anyone else reporting Apple Pay issues here or on
downdetector.com. I have a feeling the tech was being less than helpful.
I know you said there's no reason for your card to decline, but have you checked your actual/remaining credit limit (credit limit - current balance - pending charges/holds)? If you go over this, the card can be declined. Another thing to check is to make sure the name and billing address is set up exactly the same as what's on record for the card. If you can, try charging a smaller amount to see if that goes through, or a different card.