Resource not found!! Laravel 5.7

I have in my web.php the following routes:

Route::get('admin', ['as' => 'admin.login', 'uses' => 'AdminController@login']);
Route::post('admin', ['as' => 'admin.postLogin', 'uses' => 'AdminController@postLogin']);
Route::group(['middleware' => 'isAdmin'], function () {
  Route::get('admin/transactions', ['as' => 'admin.transactions', 'uses' => 'AdminController@transactions']); // problem is when i redirect to this route
});

and my controller as follow:

public function postLogin(Request $request){
  //some logic
  return Redirect::to('admin/transactions');
}

and the transaction action:

public function transactions(){
    dd('ok');
}

but i still get Resource not found!! why?

Can anybody help me?

Note!!: I have other routes working fine so i don't think it's an .htaccess problem

via Chebli Mohamed