Creates a new webhook scoped to a specific event. Event-level webhooks fire only for the specified trigger within this event. The webhook URL must be a valid HTTP(S) URL and must be unique per trigger within the same event. Requires the event to have webhooks enabled; returns an error if webhooks are disabled.

Note: administrative_area_ids conditions are not supported for event-level webhooks. Use account-level webhooks to apply administrative area filtering.