Power BI API Unauthorized: ServicePrincipalIsNotAllowedByTenantAdminSwitch despite switched on.

[lokane]

Following the PowerBI-Developer-Samples -> .NET Framework -> Embed for your customers sample, I am using Power BI API and the response is a 401 error with a 'X-PowerBI-Error-Info' header with value 'ServicePrincipalIsNotAllowedByTenantAdminSwitch'. I have followed all steps in Embed Power BI content with service principal and an application secret document, in particular step 3 handles this specific scenario of allowing service principals by tenant. To clarify, I am trying to use the Power BI API using service principals.