# Unknown application ID

Resolve unknown application ID errors.

The `X-App-Id` value is a valid UUID but does not match any registered [application](/explanation/application).

Verify the application ID against the one shown in the [application settings](https://app.croct.com/redirect/organizations/-organization-/workspaces/-workspace-/applications/-application-/settings).

## 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/unknown-public-id",
  "title": "The application ID is unknown.",
  "status": 401,
  "detail": "The provided application public ID does not exist.",
  "instance": "/client/web/content"
}
```