Getting 403 - API is not accessible for application when calling Power BI API Get Pages

[GoodPanos]

I have registered an app (service principal) with App.Read.All, Report.Read.All and Workspace.Read.All permissions. The app has member access to the four workspaces in need.

When I call:

GET https://api.powerbi.com/v1.0/myorg/groups/{groupId}/reports 

It works successfully. All reports are acquired for each workspace.

When I call:

GET https://api.powerbi.com/v1.0/myorg/reports/{reportId}/pages

I get 403 - API is not accessible for application.

When I call:

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

I get the page metadata for some reports and for others I get 401 (DENY) error.

When I test the above api call at the Power BI REST APIs website with the failed report with my account it works. Mind you I only have view access to the reports.

What am I missing??? I don't understand why ...groups/{groupId}/reports/{reportId}/pages works for some reports and not others.

[GoodPanos · Accepted solution]

Resolved! Turns out that some of the reports had their datasource on another workspace. Once we granted access to those workspaces to the service principal account, the API calls ran successfully.