#4 just provided this info:

"I kept getting redirected back to the cart after I selected the Amazon Pay without receiving any notice at all. there was no information about if the order payment was denied or anything else.
So, after 2 Amazon attempts, I decided to try my credit card, and I was able to complete the order."

Its as if something changed at Stripe and now Payments other than credit cards, fail to create an order in Zen