Why are GoHighLevel appointment start and end times blank in my webhook?

Fix our GoHighLevel Outbound Webhook workflow where appointment.start_time and appointment.end_time arrive blank:
1. Check the workflow trigger and replace any Contact-scoped trigger (like Contact Tag Added or Opportunity Changed) with "Appointment Status" (Status = Confirmed) or "Customer Booked Appointment".
2. Add a native "Format Data — Date/Time Formatter" action before the Outbound Webhook to format {{appointment.start_time}} and {{appointment.end_time}} as ISO-8601 timestamps.
3. Map the formatted timestamps into explicit Custom Data keys on the Outbound Webhook action.

# 1. MCP Tool Call (ghl-crm-mcp)
{
  "tool": "workflows_create_from_recipe",
  "arguments": {
    "location_id": "<YOUR_LOCATION_ID>",
    "recipe": "appointment_iso_timestamp_webhook",
    "trigger": "appointment_status_confirmed",
    "dry_run": true
  }
}

# 2. Or run via ghl-crm Rust CLI
ghl-crm workflows apply-recipe --location-id <YOUR_LOCATION_ID> --recipe appointment-iso-webhook --dry-run