curl --request DELETE \
  --url http://localhost:8080/api/calls/{callId} \
  --header 'X-API-KEY: <api-key>' \
  --header 'X-API-SECRET: <api-key>'

{
  "message": "Scheduled call cancelled successfully - converted to regular call",
  "status": "success",
  "error": null,
  "data": {
    "operation": "schedule_cancelled",
    "organization_id": "org-789",
    "call_id": "call_bf2a9c7d-4e5f-4318-9b2a-8d7c6e4f1a0b",
    "cancelled_scheduled_timestamp": 1748460000,
    "call": {
      "call_id": "call_bf2a9c7d-4e5f-4318-9b2a-8d7c6e4f1a0b",
      "metadata": {},
      "events": [
        {
          "timestamp": 1748452100000,
          "event": "Scheduled call cancelled - converted to regular call",
          "data": {
            "previous_scheduled_timestamp": 1748460000,
            "cancelled_at": 1748452100,
            "endpoint_used": "/schedule DELETE"
          }
        }
      ]
    }
  }
}