Always get "InternalServerError" when getting attendee report of a live event

I would like to get attendee report of a live event. When I send a GET request to https://graph.microsoft.com/beta//users/{userId}/onlineMeetings/{meetingId}/attendeeReport, I always get the following "InternalServerError" as follows:

{
    "error": {
        "code": "InternalServerError",
        "message": "Object reference not set to an instance of an object.",
        "innerError": {
            "date": "2021-01-20T07:51:13",
            "request-id": "89d14fa2-5385-4c8a-86c6-ee8d999e0b6c",
            "client-request-id": "89d14fa2-5385-4c8a-86c6-ee8d999e0b6c"
        }
    }
}

Have you had any similar experience and how did you resolve it?

By the way, I rest assured that my authorization token is not expired and both userId and meetingId are correct.

Thank you very much.