Microsoft 365 user names should always be specified as email addresses: This error indicates that the specified Microsoft 365 user name is invalid. Microsoft 365 requires users to log in with an email address, not a user name as in "John Doe" or "domain\johndoe".
We recommend the following:
- If using administrative credentials for Microsoft 365, check the admin user name specified on your project.
- If not using administrative credentials for Microsoft 365, check the mailbox owner user name specified on the mailbox.
- In all cases, make sure the user name work when logging in at https://login.microsoftonline.com.