iTunes Infinite Sign In Loop

I am trying to make an iTunes purchase via the Windows 10 PC app and get stuck in a repeated sign in loop. When asked to verify payment info and to verify billing info I am prompted for my password again which I enter, iTunes churns away for a while and then dumps me back onto my account screen with no error message . When I click Manage Payments I am prompted for my password again and then sent back to my account screen. The same happens when I click Edit for the payment info. I never receive an error message. This happens over and over no matter how many times I supply my login credentials.

I am currently logged in to iTunes on both my PC and iPhone. My internet connection is fine. My software is all up to date (verified).

What can I do to fix this?