Unauthorized response getting reports through groups endpoint of API

I'm using the Power API REST API to first retrieve groups that the logged in user has access to, and then to retrieve reports within those groups.  I can successfully retrieve reports through the https://api.powerbi.com/v1.0/myorg/reports endpoint, but if I make the request through the https://api.powerbi.com/v1.0/myorg/groups/{group_id}/reports endpoint with any of the retrieved group id's, I get a 401 - Unauthorized response.  I am sending the access token as an authorization header using the "Bearer {token}" format, the same as when I successfully retrieve reports independent of the group id.  Can anyone suggest what the problem is here?  Thanks in advance!