Apple Pay: "Cannot complete payment"

I have Apple Pay set up on my Mac and my iPhone and I went to check out on my Mac (the website expressly gives Apple Pay as an option at checkout) and my Mac sent it to my iPhone to approve and I double-clicked to purchase and it kept saying "Cannot complete payment."

I double-checked my name, billing address, email, phone number for the card in Settings and everything lines up with the bank. I'm not sure what the problem is -- any tips would be greatly appreciated!