"Insufficient privileges to complete the operation" while using Graph API

Hello, everyone!

I'm trying to use the Microsoft Graph API with App Authentication to assign an Product License to a user. 

My App has the App permissions "LicenseAssignment.ReadWrite.All", "Directory.ReadWrite.All" and "User.ReadWrite.All".

https://graph.microsoft.com/v1.0/users/$upn/assignLicense

{
    "error": {
        "code": "Authorization_RequestDenied",
        "message": "Insufficient privileges to complete the operation.",
        "innerError": {
            "date": "2025-03-19T08:17:35",
            "request-id": "c368027b-6462-472f-a726-a9b04b26e11e",
            "client-request-id": "c368027b-6462-472f-a726-a9b04b26e11e"
        }
    }
}

My request body looks as follows:

{
  "addLicenses": [
    {
      "disabledPlans": [],
      "skuId": "..."
    }
  ],
  "removeLicenses": []
}

For assigning a license, I got teams(community) list, and members list.

I hope for your selfless help.