Azure Domain Services - Invalid Credentials on NetJoin

I am trying to connect a Windows Server 2012 R2 Azure Server to a Directory Services enabled Azure Domain. When I attempt to Join this Server to the Azure Domain I get Invalid Username/Password.

When I ping the Domain or the IP I get responses.

I have created the "AAD DC Administrators" group and added a Service admin user and the Azure Subscription Admin account to. I am unable to join using either of there Credentials.

This is also a [name] Domain.

Any ideas would be great.