# Invalid API key

Resolve invalid API key errors.

The `X-Api-Key` header was provided but its value is not a valid UUID.

[API keys](/explanation/application/api-keys) must be [version 4 UUIDs](https://www.rfc-editor.org/rfc/rfc4122).

## Response

All error responses follow the [Problem Details (RFC 9457)](/reference/api/overview#errors) format. The `type`, `title`, `status`, and `detail` fields are always present, while `instance` may be omitted depending on the API.

Here is an example of the response returned for this error:

```json
{
  "type": "https://croct.help/api/authentication/invalid-api-key",
  "title": "The API key is invalid.",
  "status": 401,
  "detail": "The provided API key is not in a valid format.",
  "instance": "/client/web/content"
}
```