使用自定义FormRequest时请求未正确发送，但在使用默认值时发送

This is my code for logging the user in using Laravel Passport:

public function login(LoginRequest $request)
{
    $email = $request->email;
    $password = $request->password;

    $request->request->add([
        'username' => $email,
        'password' => $password,
        'grant_type' => 'password',
        'client_id' => env('PASSWORD_GRANT_CLIENT_ID'),
        'client_secret' => env('PASSWORD_GRANT_CLIENT_SECRET'),
        'scope' => '*',
    ]);

    $tokenRequest = Request::create(
        env('APP_URL') . '/oauth/token',
        'post'
    );

    $response = Route::dispatch($tokenRequest);

    return $response;
}

The LoginRequest class:

/**
 * Determine if the user is authorized to make this request.
 *
 * @return bool
 */
public function authorize()
{
    return true;
}

/**
 * Get the validation rules that apply to the request.
 *
 * @return array
 */
public function rules()
{
    return [
        'email' => 'required|string|email|max:255',
        'password' => 'required|min:6',
    ];
}

When I try to login using Insomnia client, the following is returned:

{
    "error": "unsupported_grant_type",
    "message": "The authorization grant type is not supported by the 
    authorization server.",
    "hint": "Check that all required parameters have been provided"
}

I have tried returning the $request from the login function instead of $response, yet what it returns is what's exactly sent from the function so I know the problem is not that.

What was more confusing is that if I replace the LoginRequest injection inside the login method with the default Request, the function works fine.

Anyone know how this could be resolved?