CAUSE: The on-premises AD DS is no longer available. Therefore, you can’t manage or delete the object from the on-premises environment.
Solution:
Install the Azure Active Directory Module for Windows PowerShell. For more info, go to the following Microsoft website: Manage Azure AD using Windows PowerShell
Connect to Azure AD by using Windows PowerShell.
Disable directory synchronization. To do this, type the following cmdlet, and then press Enter: Set-MsolDirSyncEnabled –EnableDirSync $false
Check that directory synchronization was fully disabled by using the Windows PowerShell. To do this, run the following cmdlet periodically: (Get-MSOLCompanyInformation).DirectorySynchronizationEnabled This cmdlet will return True or False. Continue to run this cmdlet periodically until it returns False, and then go to the next step. Note: It may take 72 hours for deactivation to be completed. The time depends on the number of objects that are in your cloud service subscription account.
As mentioned above, it may take upto 72 hours to disable the synchronization. You can check the status with the following command (Get-MSOLCompanyInformation).DirectorySynchronizationStatus The result should show ‘Disabled’. In case it displays ‘Pending Disable’, you need to wait as it has not yet completely disabled the sync.