> For clean Markdown of any page, append .md to the page URL.
> For a complete documentation index, see https://docs.usglobalmail.com/llms.txt.
> For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://docs.usglobalmail.com/_mcp/server.

# Validation error

Returned as `application/problem+json` with `code` `validation_error` and HTTP status `422`.

The request was well-formed, but one or more fields failed validation. The `errors` array lists each failure by field.

## Common causes

* A required field is missing.
* A field has the wrong type or an out-of-range value.
* The `cursor` parameter is malformed.

## How to resolve

* Inspect `errors[]`, fix the named fields, and resend.
* Field names use the request’s JSON paths.

## Example

```json
{
  "type": "https://docs.usglobalmail.com/api/problems/validation_error",
  "title": "Your request parameters did not validate.",
  "status": 422,
  "code": "validation_error",
  "request_id": "req_8f3c2a1b9d",
  "instance": "/v1/mails",
  "errors": [
    {
      "field": "is_read",
      "message": "must be a boolean"
    }
  ]
}
```

> **Note**
>
> Retrying without changing the request will not help — fix the request first.

See also: [Errors](/guides/core-concepts/errors).