> 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.

# Bad request

Returned as `application/problem+json` with `code` `bad_request` and HTTP status `400`.

The request couldn't be parsed at all — its body, headers, or query string were malformed. This is distinct from [`validation_error`](/api/problems/validation_error), where the request parses but a field is invalid.

## Common causes

* The request body is not valid JSON.
* A query parameter is malformed and cannot be parsed.
* The request is structurally broken in a way the schema cannot accept.

## How to resolve

* Verify the body is valid JSON and `Content-Type: application/json` is set.
* Check query-parameter formats against the [API Reference](/api/api-reference).

## Example

```json
{
  "type": "https://docs.usglobalmail.com/api/problems/bad_request",
  "title": "The request was malformed.",
  "status": 400,
  "code": "bad_request",
  "request_id": "req_8f3c2a1b9d",
  "instance": "/v1/mails"
}
```

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