> ## Documentation Index
> Fetch the complete documentation index at: https://docs.e6data.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Errors and recovery

> Read the status and error code together. A failed HTTP exchange does not always prove that a mutation was rejected.

How-to guideApplies to: Unified engine deployments

Read the status and error code together. A failed HTTP exchange does not always prove that a mutation was rejected.

## Error body

```json theme={"theme":{"light":"github-light","dark":"github-dark"}}
{
  "error": {
    "code": "revision_conflict",
    "message": "The resource changed; refresh before trying again"
  }
}
```

Some domain responses add structured validation details. Response examples show the server's response, including non-JSON proxy errors. Large previews are limited.

| Status | Typical meaning | Next action |
| - | - | - |
| 400 | Invalid request or unsupported fields. | Correct the named field or syntax. |
| 403 | Access or a configured action is denied. | Check the deployment's access context. |
| 404 | Resource not found. | Check its identity and scope. |
| 405 | Method not allowed. | Check the method for that route. |
| 409 | Identity conflict, revision conflict, busy resource, or result not ready. | Read the error code and current state. |
| 410 | Closed session or expired results. | Use available history; do not assume rows remain. |
| 413 | Request or response exceeds a limit. | Reduce payload or page size. |
| 415 | Wrong content type. | Send application/json where required. |
| 422 | Domain validation failed, including configuration edits. | Inspect validation details. |
| 501 | Operation or optional service is unavailable on this instance. | Check capabilities and supported features. |
| 503 | Dependency unavailable or outcome unknown. | Preserve request identity and inspect state before retrying. |

These are common mappings, not a promise that every endpoint returns every status. A gateway can add its own authentication or transport responses.

## Separate request and execution failures

A 202 response can later lead to a failed operation. A 200 status read can report a Failed run. A notification can fail after a successful data workflow. Follow the relevant resource's state and failure details.

## Collect useful evidence

Keep the resolved request URL, method, non-secret input, request identity, resource IDs, revision, HTTP status, error code, and timestamps. Correlate operation, run, task, attempt, and audit data as appropriate.

See [Request identity](https://docs.e6data.com/transformation/http/request-identity.md) before repeating a mutation after a lost response.


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