Originally Posted by hogo74

Thanks for the responses. I'm happy to report that after reading through the related discussion on this tripadvisor thread, I was able to use my US-issued Amex to complete the payment. I would never have thought of trying it because Amex isn't listed as one of the payment options, they only show Visa and MC on the credit card payment screen. But you can just type in your Amex info (using the four digits on the front as CVV of course) - the image showing the stylized card with your info as you type it in actually changes to an Amex logo. After hitting submit, the pop-up window that just showed "please used a 3D Secure card" when trying to use a Visa/MC now displayed "Amex Safekey" (which is their implementation of 3D Secure, I guess) for a while before the transaction was approved. I still wasn't asked for any 2FA from the Amex side, but I guess with this Amex card the payment request was actually sent on to the card issuer who approve it rather than being blocked outright by the vendor.