Why as a co-administrator of a subscription am I unable to edit the Active Directory?

Question

A customer made me a co-administrator of his Azure subscription. However, I am unable to edit his Active Directory, ie add/edit users, create applications, etc.

Why

Answer 1

Both answers above seem to be correct in it's own way.

As a starter subscription administrator does not automatically make you an Azure AD administrator. You'd need explicit role grant on the target Azure AD.

Second aspect is the type of the account used. If it's in current Azure AD or Microsoft Live account all is well. In case that account is part of an external Azure AD, by default user type is "Guest"(can login, but cannot control event if assigned "Global admin"). Therefore PowerShell commands highlighted above should be executed to change user type to "Member".

Some more helpful info can be found here (it is mentioned as a Visual Studio Team Services issue, but actually applies to most Azure related services).