Account login issue

Hello.

I've had Kindle 1.17 and Calibre 2.21 for several years now and never ran into a problem

Today I de-registered my account on Kindle because I wanted to sign in with a different account. I tried to register a new account and was unable to do so. I get the following message from the Amazon sign in screen "There was a problem. Enter a valid email or mobile number"

I've tried different accounts, resetting the password, and trying to create a new account. I eventually get the same message.

Any idea what the issue is and how I can fix it? I've uninstalled Kindle and reinstalled it. Thanks

Using Kindle 1.17 on Windows 10