You try to add a subdomain to an existing domain in a Microsoft cloud service such as Office 365, Microsoft Intune, or Microsoft Azure by using the New-MSOLDomain cmdlet. However, you receive the following error message:
New-MsolDomain: Unable to add this domain. It is a subdomain and its authentication type is different from the authentication type of the root domain.
This issue occurs if you try to use the New-MSOLDomain cmdlet to add a subdomain to an existing domain that's set up for federated authentication. The New-MSOLDomain cmdlet tries to add the subdomain as a standard authentication domain.
To add a subdomain to a domain that's set up for federated authentication, follow these steps:
Connect to Azure Active Directory (Azure AD) by using Windows PowerShell. For more info, go to the following Microsoft website:
Microsoft Azure cloud services, Microsoft Azure Active Directory, Microsoft Office 365, Microsoft Intune, CRM Online via Office 365 E Plans, Microsoft Azure Recovery Services, Office 365 User and Domain Management, Office 365 Identity Management