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

# Request validation

> What every request is checked for, and the errors you may receive.

Every request is validated in the following order. The first check that fails determines the
response:

| Order | Check                                             | Failure                                             |
| ----- | ------------------------------------------------- | --------------------------------------------------- |
| 1     | Valid API key                                     | `401`                                               |
| 2     | API access enabled for your plan                  | `403 api_access_disabled`                           |
| 3     | Access to the requested resource enabled          | `403 api_module_access_disabled`                    |
| 4     | Not currently rate limited or temporarily blocked | `429 rate_limit_exceeded`                           |
| 5     | Request payload is valid                          | `4xx` (see [Response format](/api/response-format)) |

See [HTTP status codes](/api/errors) for the full list and [Rate limits](/api/rate-limits) for
`429` handling.