Graph API 1.0, create online meeting, videoTeleconferenceId and audioConferencing are null

Hi Team,

Can you please help on below issue? Thanks in advance.

I tried with following URL to create a online meeting:

https://graph.microsoft.com/v1.0/users/[system/onlineMeetings

and got following response:

{
"id": "MSo5OGVjZmYxNi1kYTM0LTRhYmMtOTFiMC1iN2QwNTVmNzhkZDUqMCoqMTk6bWVldGluZ19ORFEyWldSak1Ua3RaakV3WlMwME9USm1MV0k1WVdVdFpUTmlZMk5oTXpjME9HUTNAdGhyZWFkLnYy",
"creationDateTime": "2021-08-24T18:22:59.9081502Z",
"startDateTime": "2021-08-24T18:22:59.1863439Z",
...
"videoTeleconferenceId": null,
"externalId": null,
"broadcastSettings": null,
"audioConferencing": null,
...
}

The videoTeleconferenceId and audioConferencing are null,  why these 2 values are null? Any specific requirement we need to do on our side to get these 2 values back?

thanks very much