I am trying to log into our hosted Exchange Admin account to troubleshoot an issue with emails randomly not being delivered. The global account (with an onmicrosoft.com) address requires be to set up MFA through the Authenticator app, but I receive the error "The account you're trying to add is not valid at this time. Contact your admin to fix this issue (uniqueness validation)."
I have tried using a different authenticator app, deleting all of the other Azure account profiles from the app, using a text message code instead of the app code.
Since I'm not able to log into the admin account, I can't open a support ticket or review any of the account settings.
I did find this ticket which mentions a possible email address conflict on the admin account with a different user, but since I can't log into the admin account, I can't check that (Oct 26 23 update). https://learn.microsoft.com/en-us/answers/questions/1296807/mfa-user-registration-issue
Appreciate any ideas or information on how to reset admin access or how I can speak with a support person at MS who can look at the admin account to see if the above link is the issue. At this stage we have no access to manage our account licenses or users. Thank you!