Symptoms
When you sign in to Microsoft 365, you receive the following error message:
Specified tenant identifier 'undefined' is neither a valid DNS name, nor a valid external domain.
Resolution
To fix this issue, install the following hotfix update:
Workaround
To work around this issue, run the updated Setup-AzureAdForSFBControlPanel.ps1 script after applying the CU1 update when configuring Microsoft 365 authentication with MACP.
For more information, see Skype for Business Server 2019 control panel authentication script.
