HTTP 401 returned when attempting to generate embed token for report

I am trying to generate an embed token so I can embed a Power BI report into my own web application. I am using the API Embed Token - Reports GenerateTokenInGroup.

POST https://api.powerbi.com/v1.0/myorg/groups/{groupId}/reports/{reportId}/GenerateToken

I am passing in the groupId and the reportId as shown in the API. Below is a screen capture from Postman where I am setting the values.

The API response I get is 401 Unauthorized. However I have all permissions possible within Azure (see screen capture).