Ok, ok, I got it. I had to put my retry in a loop and throw an await on my server call. Got things figured out from a writeup at mozilla.org. Lawdy, I thought Microsoft's docs were bad but after my Apple Pay endeavor, Apple's docs make Msft's seem complete and concise. @aprotyas thanks for pointing me in the correct direction.

Figured out my problem. Seems supports3DS is required in the merchantCapabilities.

Any feedback regarding this error? I am experiencing the same thing when utilizing the Payment Request API.

Seems I was correct. In order to use test cards and have the test URL supplied to your verification event, you must create a sandbox account in App Store Connect and then sign in to iCloud with that account on your device.