Webhook (aka Subscription) for groups ressource changeType = created not working

HI,

I'm looking for an fast and efficiant way to get notified for new AAD groups (unified groups to be exact). I could us the groups endpoint and then do a delta query every 5 minutes. But this is not "instant". MS Graph offers their implementation of webhooks (subscriptions) to solve this problem. I've checked the github repo:

https://github.com/microsoftgraph/aspnet-webhooks-rest-sample

And it works as designed for user email messages. I've modifed the code to get a subscription for groups. Currents these are only available in the /beta version. So I changed all URL and the message example is working on the beta version. Then I changed the subscription from messages to groups. But the sample refused to work. I tried the same request using the MS Graph Explorer but also failed due to this message:

{
    "error": {
        "code": "InvalidRequest",
        "message": "Invalid 'changeType' attribute: 'created'.",
        "innerError": {
            "request-id": "9b786de2-1780-4ccf-9d1a-1243d0435ce1",
            "date": "2017-09-14T13:37:33"
        }
    }
}

The message is indicating that "created" is not supported :( The same request with "updated" is working as expected :( Permissions for the app are updated with Group.Read.All as the docs states.

This is the request:

{
  "changeType": "created",
  "clientState": "ca07f995-5f94-4a7a-903a-a6f9deb517e4",
  "notificationUrl": "https://gkm-msgraph-webhook.azurewebsites.net/notification/listen",
  "resource": "groups",
  "expirationDateTime": "2017-09-14T13:09:26.8315691+00:00"
}

 The docs are suggesting it should work (I know it is the beta hive). Any idea?

These are the docs:

https://developer.microsoft.com/en-us/graph/docs/api-reference/beta/api/subscription_post_subscriptions