Cannot use Apple Pay to make purchase on AllBirds.com?

I have attempted to make a purchase on AllBirds.com. I get a failure notice after I double-click on my iPhone. I can make Apple Pay purchases on other websites. I've tried this twice now and it fails.

• I've contacted AllBirds and they indicated no problems, no other reports of this
• I chatted with Apple who couldn't see any reason it would fail, and Apple suggested instead of Safari I try FireFox or Chrome?
  • AllBirds doesn't even show an Apple Pay option on FireFox (but they do on Safari)
  • Apple said this must be evidence that Allbirds isn't processing Apple Pay?