Error on adding subscription on events using MS Graph

Jørgen Iversen 11 Reputation points

I am using the MS graph subscription endpoint ( to add a subscription on a calendars events for some of my end users outlook accounts. For some accounts (not all) this fails with this error:

  "error": {
    "code": "ExtensionError",
    "message": "Operation: Create; Exception: [Status Code: ServiceUnavailable; Reason: Target resource 'xxxx-xxx-xxx-xxxx' hosted on database 'xxxx-xxx-xxx-xxxx' is currently on backend 'Unknown']",
    "innerError": {
      "date": "2021-05-31T08:27:37",
      "request-id": "c7c38d7a-617c-4601-9684-0f924e86248a",
      "client-request-id": "c7c38d7a-617c-4601-9684-0f924e86248a"

Just before adding the subscription my code have been able to add a new event to the same calendar, so I think that my access token has the right permissions to access the calendar. So I don't understand how I can get an "ExtensionError"?

Here is the C# code that I run to try to add the subscription:

var subscription = new Subscription
    ChangeType = "created,updated,deleted",
    NotificationUrl = GetNotificationUrl(),
    Resource = $"me/calendars/{calendarId}/events",
    ExpirationDateTime = DateTimeOffset.Now.AddHours(70),
    ClientState = clientState,

await graphServiceClient
    .Header("Prefer", $"IdType=\"ImmutableId\"")
Microsoft Graph
Microsoft Graph
A Microsoft programmability model that exposes REST APIs and client libraries to access data on Microsoft 365 services.
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  1. Sibi Sharanyan 21 Reputation points

    Running through the same issue with Outlook calendars, Any way tor esolve this ?

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  2. David P 1 Reputation point

    I fixed this by removing the "clientState" property in my request body. I was using json escaped body as a string, so maybe the API was having a tough time dealing with it.

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