PowerBI embedded and access denied

Hey

I have followed this guide on learn.microsoft.com

Get started with Power BI Embedded - Power BI | Microsoft Learn

Onboarding Embed Tool (powerbi.com)

Using ServicePrincipal - I have entered the applicationSecret, tenant og changed the authenticationType to "ServicePrincipal" in the sample application - but I get an access denied.

 Status: Unauthorized (401)
Response: {"error":{"code":"PowerBINotAuthorizedException","pbi.error":{"code":"PowerBINotAuthorizedException","parameters":{},"details":[],"exceptionCulprit":1}}}

What am I missing?

(When using the masteruser it works.)