Retrieve batch

{
  "id": "batch_abc123",
  "object": "batch",
  "endpoint": "/v1/completions",
  "errors": null,
  "input_file_id": "file-abc123",
  "completion_window": "24h",
  "status": "completed",
  "output_file_id": "file-cvaTdG",
  "error_file_id": "file-HOWS94",
  "created_at": 1711471533,
  "in_progress_at": 1711471538,
  "expires_at": 1711557933,
  "finalizing_at": 1711493133,
  "completed_at": 1711493163,
  "failed_at": null,
  "expired_at": null,
  "cancelling_at": null,
  "cancelled_at": null,
  "request_counts": {
    "total": 100,
    "completed": 95,
    "failed": 5
  },
  "metadata": {
    "customer_id": "user_123456789",
    "batch_description": "Nightly eval job",
  }
}