Can't add user to D365 tenant unless it is Global Administrator in O365 Admin Center

Hi

We want to add a user to our Dynamic 365 instance to be used by a third party developer. 

We created the user in O365 Admin Center and gave it license for "Dynamics 365 for Sales Enterprise Edition".

We also expand roles in for the user in O365 Admin Center and give it "Dynamics 365 service administrator".

The user does not appear in Settings -> Security -> Users however. 

The only way that any user appears among D365 users is if it is assigned the "Global Administrator" role in O365 Admin Center which is against security policy. 

Does anyone know how this should be setup to provide administrative access to D365 for a third party developer that doesn't need "Global Administrator" role in O365 Admin Center ?

Thank you for any assistance in advance. 

Regards

David