Hello Allan Deyoung,
Thanks for reaching out!
As per my investigation, you can't retrieve the attendanceReports of an onlineMeeting if you are not the organizer for that specific onlineMeeting. Additionally, with delegated permissions only /me endpoint is supported. Please use Application Permission instead.
To use application permission for this API, tenant administrators must create an application access policy and grant it to a user. This authorizes the app configured in the policy to fetch online meetings and/or online meeting artifacts on behalf of that user (with the user ID specified in the request path). For more details, see Allow applications to access online meetings on behalf of a user.
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