Laravel redirect failed login: Method loginUsername does not exist

I am using Laravel 5.6, and tried to override the sendFailedLoginResponse method in LoginController, but i get the following error upon bad credentials:

Method App\Http\Controllers\Auth\LoginController::loginUsername does not exist.

I have two login forms on my website (on '/home' and '/login'). I want to redirect all failed attempts to '/login'. This is my code:

namespace App\Http\Controllers\Auth;

use App\Http\Controllers\Controller;
use Illuminate\Foundation\Auth\AuthenticatesUsers;

use Illuminate\Http\Request;

class LoginController extends Controller
{
    use AuthenticatesUsers;
    protected $redirectTo = '/home';

    public function __construct()
    {
        $this->middleware('guest')->except('logout');
    }

    protected function sendFailedLoginResponse(Request $request)
    {
        return redirect('login')
            ->withInput($request->only($this->loginUsername(), 'remember'))
            ->withErrors([
                $this->loginUsername() => $this->getFailedLoginMessage(),
            ]);
    }
}

via Chebli Mohamed