> For the complete documentation index, see [llms.txt](https://docs.moderncollections.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.moderncollections.io/rest-api-explorer/welcome-to-the-modern-collections-api/error-envelope.md).

# Error envelope

All errors return a consistent JSON envelope:

```json
{
  "error": {
    "code": "validation_failed",
    "category": "invalid_request",
    "message": "debtor.state is required",
    "request_id": "req_01HZX2Y3K8N5R7Q9V4M6P1C0"
  }
}
```

| Status | Meaning                                                                                                                   |
| ------ | ------------------------------------------------------------------------------------------------------------------------- |
| `400`  | Bad request — fix the request body or query parameters.                                                                   |
| `401`  | Unauthorized — missing or invalid API key.                                                                                |
| `403`  | Forbidden — the key lacks permission for this resource.                                                                   |
| `404`  | Not found — the resource does not exist.                                                                                  |
| `409`  | Conflict — typically a duplicate `invoice_number` for the same debtor.                                                    |
| `422`  | Compliance refusal — the request violates a compliance gate.                                                              |
| `429`  | Rate limited — honor the `Retry-After` header.                                                                            |
| `5xx`  | Server error — retry with backoff. Persistent failures surface in our [status page](https://status.moderncollections.io). |

{% hint style="warning" %}
Always log the `request_id` from the response on your side. It's the fastest way for our support team to triage an issue.
{% endhint %}


---

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