When creating webhook subscriptions during provisioning using the 'on-provision webhook' resource type, the event URL for webhooks can be accessed by interpolating {webhookCallbackUrl} within the body that is sent to the provider.
Here is an example body used in a POST /webhooks call (on-provision webhook), please note the contents of the body will be provider specific:
{ "name": "My Cool Webhook", "url": "{webhookCallbackUrl}", "events": [ "project_created", "project_updated", "project_deleted", "user_created", "user_updated", "user_deleted", "comment_created", "comment_updated", "comment_deleted", "jira:issue_created", "jira:issue_updated", "jira:issue_deleted", "worklog_updated", "worklog_created" ], "excludeBody" : false }