Apple Watch - Apple Pay setup error when clicking any button

I’m trying to set up Apple Pay on my Series 4, and getting the below error message before I even get to the point when I add in my card.


I get it a few seconds after tapping the “Add Card” link to add a new card, and I get it when I tap the “Add” button next to the cards it recognizes from my iPhone.

I’ve unpaired and re-paired 3 times now, twice setting up from backup and once setting up as a new Watch. I’ve removed cards on the phone and re-added them. I’ve turned off iCloud and turned it back on. Nothing has helped. This is my third Watch, and the first time I’ve had Apple Pay issues.

Before I chalk this up to a faulty Watch and before I get sucked into a lengthy support chat with Apple, does anyone have any ideas? Thanks!