Help, I'm stuck in an Apple payment verification loop!

Help, I'm stuck in an Apple payment verification loop!

My iPhone can't back up, as I need to upgrade my iCloud storage. When I click through to do that, and use my thumbprint to confirm payment to come from my ApplePay default card, it acts like it is done, then pops up a message saying verification required. When I click through that, it brings me right back around again. Over and over.

I have two AppleIDs set on my phone. One for the app store, my partner's account, which we share, and one for all my data, via iCloud. This is the one I'm trying to upgrade.

All help is most welcome.