this is the admin routes
Route::get('admin/home', 'AdminController@index');
Route::get('admin', 'Admin\LoginController@showLoginForm')->name('login.admin');
Route::post('admin', 'Admin\LoginController@login');
LoginController
public function __construct()
{
    $this->middleware('guest:admin')->except('logout');
}
public function showLoginForm() {
    return view('admin.login');
}
/**
 * Get the guard to be used during authentication.
 *
 * @return \Illuminate\Contracts\Auth\StatefulGuard
 */
protected function guard()
{
    return Auth::guard('admin');
}
layouts blade
<a class="dropdown-item" href="{{ route('login.admin') }}">
                                    admin login
                                </a>
if someone need to see more code to understand the error please comment
