Webhook subscription creation persistent 503 extensionError

Question

Hi support team,

In my application, for one specific customer, we are receiving the below error when trying to create a webhook subscription to subscribe to outlook calendar changes (https://learn.microsoft.com/en-us/graph/api/subscription-post-subscriptions?view=graph-rest-1.0&tabs=http)

We are trying to subscribe to the following resource: /me/events

The authorization flow completes successfully and other endpoints such as GET, POST events works perfectly fine.

This error has persisted for 4 days already over 10 times so I don't think it is ephemeral.

May you please investigate the specific request id and let us know why we are receiving these errors? We are using the python sdk.

Request id: 4b576992-3739-4d33-9d7c-db4972e3bd2e

Please note the account that owns the oauth token is managed by a MSP (managed service provider)

msgraph.generated.models.o_data_errors.o_data_error.ODataError: 
        APIError
        Code: 503
        message: None
        error: MainError(additional_data={}, code='ExtensionError', details=None, inner_error=InnerError(additional_data={}, client_request_id='677d8d97-a7fd-41e2-9c85-64443a9e8f69', date=datetime.datetime(2025, 9, 1, 2, 48, 58), odata_type=None, request_id='4b576992-3739-4d33-9d7c-db4972e3bd2e'), message="Operation: Create; Exception: [Status Code: ServiceUnavailable; Reason: Target resource '00034001-a43d-d47d-0000-000000000000' hosted on database '1865ddf5-de31-4451-8855-808008d9a507' is currently on backend 'Unknown']", target=None)

Thanks,

Calvin