Hi @tomaskebrle ,
Thank you for reaching out to the Microsoft Fabric Community.
The 500 UnknownError encountered when invoking the Users - List Access Entities admin endpoint with a service principal is likely due to permission or configuration issues. After enabling admin API access according to Microsoft’s documentation, please ensure the service principal has the Fabric Admin role, appropriate API permissions, and admin consent granted. Also, verify that the user ID or UPN you are providing is valid, as an invalid or malformed value can result in a 500 error. Since this endpoint is in preview, occasional instability or limited error messaging may occur. Additionally, Conditional Access policies within your organization could silently block service principal requests, leading to unexplained errors.
For troubleshooting, consider testing the endpoint with an admin user token to determine if the issue is specific to the service principal. Confirm the user ID being used, and utilize tools such as Microsoft Graph Explorer or Azure CLI to review the service principal’s permissions. Reviewing Entra ID (Azure AD) logs may help identify blocked or failed token requests, and testing with Postman or Fiddler can provide further insight from response headers. If the problem persists after these checks, it is advisable to contact Microsoft support and provide the request details, including activity ID and timestamp.
Microsoft Entra Conditional Access for workload identities - Microsoft Entra ID | Microsoft Learn
Hope this helps. Please reach out for further assistance.
If this post helps, then please consider to Accept as the solution to help the other members find it more quickly and a kudos would be appreciated.
Thank you.
