If you receive the below error when configuring Microsoft 365 Server-side, you must disable MFA for your admin account in Microsoft 365. You should also ensure that "Require MFA for admins" and "Block legacy authentication" in your Entra ID (Azure AD) Conditional Access - Policies setting are disabled.
How to disable MFA for specific Microsoft 365 admin account
How to disable "Require MFA for admins" and "Block legacy authentication" policies in Entra ID (Azure AD)
You can also temporarily disable the"Security defaults" under Azure AD
