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

# Errors

> Stable machine codes — branch on code, never on message text.

Errors are JSON with a human message and, where it matters, a stable machine code:

```json theme={null}
{ "error": "This data requires a Pro subscription.", "code": "upgrade_required" }
```

| Status | Code               | Meaning                                                       | Do                                                 |
| ------ | ------------------ | ------------------------------------------------------------- | -------------------------------------------------- |
| 400    | —                  | Invalid parameter                                             | Fix the request; the message says which parameter. |
| 401    | `unauthenticated`  | Key missing, revoked, malformed — or an expired session token | Supply a valid key. Don't retry in a loop.         |
| 402    | `upgrade_required` | Pro-only surface                                              | Upgrade, or tell your user.                        |
| 404    | —                  | Unknown company, country, symbol, period or accession         | Re-resolve via `/search`.                          |
| 409    | `key_limit`        | Too many active keys                                          | Revoke one first.                                  |
| 429    | `rate_limited`     | Per-minute or per-day ceiling                                 | Sleep `Retry-After` seconds.                       |
| 429    | `quota_exceeded`   | Monthly quota spent                                           | Wait for `resets_at`, or upgrade.                  |
| 5xx    | —                  | Server fault                                                  | Retry with backoff; report if persistent.          |

Message strings are for humans and may change; codes are the contract.