# Error Codes

All API errors follow a consistent JSON format:

```json
{
  "error": {
    "code": "ERROR_CODE",
    "message": "Human-readable description"
  }
}
```

## Complete Error Reference

### 400 — Bad Request

| Code                     | Description                                                                              |
| ------------------------ | ---------------------------------------------------------------------------------------- |
| `INVALID_FIELD`          | Field value is invalid (empty, wrong characters, too long)                               |
| `INVALID_SEQUENCE`       | Journal entry sequence must start at 1 and increment without gaps                        |
| `INVALID_BALANCE_POLICY` | Unknown `balance_policy` value (must be `ALWAYS_POSITIVE`, `ALWAYS_NEGATIVE`, or `NONE`) |

### 401 — Unauthorized

| Code           | Description                                             |
| -------------- | ------------------------------------------------------- |
| `UNAUTHORIZED` | Missing or invalid `X-Api-Key` / `X-Api-Secret` headers |

### 403 — Forbidden

| Code                 | Description                                              |
| -------------------- | -------------------------------------------------------- |
| `INVALID_CREDENTIAL` | `api_secret` does not match the expected HMAC derivation |

### 404 — Not Found

| Code                        | Description                                    |
| --------------------------- | ---------------------------------------------- |
| `ACCOUNT_NOT_FOUND`         | Account UUID does not exist                    |
| `JOURNAL_ENTRY_NOT_FOUND`   | Journal entry UUID does not exist              |
| `TRANSACTION_NOT_FOUND`     | Transaction UUID has no journal entries        |
| `IDEMPOTENCY_KEY_NOT_FOUND` | Key not found or expired (past configured TTL) |
| `CREDENTIAL_NOT_FOUND`      | `api_key` not found or already revoked         |

### 409 — Conflict

| Code                        | Description                                                                                   |
| --------------------------- | --------------------------------------------------------------------------------------------- |
| `DUPLICATE_IDEMPOTENCY_KEY` | Key already used within the idempotency window                                                |
| `DUPLICATE_API_KEY`         | `api_key` already exists when registering a credential                                        |
| `INTEGRITY_VIOLATION`       | Row hash mismatch — possible direct database tampering. Also blocks ledger archive operations |

### 422 — Unprocessable Entity

| Code                 | Description                                                               |
| -------------------- | ------------------------------------------------------------------------- |
| `INSUFFICIENT_FUNDS` | `ALWAYS_POSITIVE` policy violated — balance would go below 0              |
| `INVALID_BALANCE`    | `ALWAYS_NEGATIVE` policy violated — balance would go above 0              |
| `ASSET_MISMATCH`     | Journal entry's declared asset does not match one of the account's assets |

### 500 — Internal Server Error

| Code             | Description             |
| ---------------- | ----------------------- |
| `INTERNAL_ERROR` | Unexpected server error |

## Handling Errors

### Retryable Errors

* **500 `INTERNAL_ERROR`** — may be transient; retry with backoff
* **Network timeouts** — the transaction may or may not have been committed; check `GET /idempotency/:key` or `GET /recovery` before retrying

### Non-Retryable Errors

* **400** errors — fix the request payload
* **401** — check your credentials
* **403** — the credential pair is invalid; regenerate from the Console
* **404** — the resource does not exist
* **409 `DUPLICATE_IDEMPOTENCY_KEY`** — the transaction was already processed; query `GET /idempotency/:key` for the original response
* **409 `INTEGRITY_VIOLATION`** — contact support; indicates database tampering
* **422** — business rule violation; adjust the transaction (add funds, fix asset, etc.)

### Reconciliation After Timeouts

If your request times out and you don't know if the transaction was committed:

1. Query `GET /idempotency/<your-key>` — if it returns 200, the transaction was committed
2. If it returns 404, the transaction was **not** committed — safe to retry with the same key
3. After a server restart, use `GET /recovery` to check the last batch before the restart


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