Can't view license info via service principal using AzureAD powershell module

Question

I'm not new to powershell or AzureAD, but I am new to the AzureAD powershell module, service principals, Applications, app registrations, and the Microsoft Graph API. As an admin vs a dev, nearly everything about azure applications is greek to me.
However, with new cybersecurity requirements wanting MFA on everything I thought it was time to write some powershell using a service principal instead of a username and password.

Initially, I'm just looking to gather the list of assigned O365 licenses.

I created an app registration, which seems to have created an application and service principal.
I went into the api permissions on my app registration/application and granted Microsoft Graph API LicenseAssignment.ReadWrite.All , said Yes as an Administrator.
I created a self signed cert and uploaded it to my app registration/application
I got the AzureAD module, connected to my tenant using my application/service principal and its certificate.

I try running Get-AzureADSubscribedSku and get the following error:
Get-AzureADSubscribedSku : Error occurred while executing GetSubscribedSkus
Code: Authorization_RequestDenied
Message: Insufficient privileges to complete the operation.

What am I missing here?

Above command works fine if I sign in with a normal global admin account.

Answer 1

Try using the PS Graph SDK instead:

https://learn.microsoft.com/en-us/powershell/module/microsoft.graph.users/get-mguserlicensedetail?view=graph-powershell-beta

https://learn.microsoft.com/en-us/graph/powershell/installation

Note the AzureAD Module is being deprecated:
https://learn.microsoft.com/en-us/powershell/microsoftgraph/migration-steps?view=graph-powershell-beta