Amex is refusing to honor the credit and I'm wondering if I have a leg to stand on or if anyone else has experienced this.

I booked through amextravel.com - I am pretty sure I selected "Pay Now" on the pop-up, and this is what the booking summary showed (also you can go try booking this hotel right now and see that the pay now option still puts you in a booking that requires a deposit just like this):

The issue seems to be that verbiage at the bottom that this is a hotel deposit charged by the hotel (even though its due at the time of the booking so IDK how that's different from prepay). I was of the understanding this is common for vegas resort hotels.

However, its been over a week and the only charge I have on my card is posted & directly from the hotel (not from amex fine hotels & resorts) for $253.97 - and thus the FHR credit is not going to trigger.

The terms on the FHR credit state "To receive the statement credits, an eligible Card Member must make a new booking using their eligible Card through American Express Travel on or after July 1st, 2021, that is prepaid (referred to as "Pay Now" on amextravel.com and the Amex App), for a qualifying stay at an available, participating Fine Hotels + Resorts or The Hotel Collection property."

I asked an amextravel rep about this, and they said EVEN if you click "Pay Now" the booking can still change to a non-prepaid one - this is my only guess what is going on here. But this is insane that you follow the terms as best you can and still get screwed by amex. If I click pay now, how is this my fault? Am I being unreasonable about this?