Error "Failed to return the service configuration" when creating Webhook

[julian_svcs]

I am trying to create a webhook on my feature service in ArcGIS Enterprise. I have added the ChangeTracking capability. When I try and create the webhook nothing is added. When I look at the ArcGIS Server logs I have two WARNINGS when I try and create the webhook:

I am able to create a Portal webhook.

Thanks for any assistance with this.

Julian.