Myth/Auth - Routing problem

My problem is of a similar nature, so I did not begin to create a new topic.
I still use modular code, it is very convenient. But now I am faced with an incomprehensible problem.

I have a user module, in its config there is a route that consists of a simple group:

PHP Code:

$routes->group('user', ['namespace' => 'Modules\User\Controllers'], function($routes)
{

    $routes->get('/',       'User::index');
    $routes->post('add',    'User::createUser');
}); 


After my form(method="POST") located at the address, site/user/, sends data to the address site/user/add, a message appears with the following text:

Code:

404 - File Not Found
Controller or its method is not found: User::add

It turns out that the get method works and the post does not ... 

Tell me what is my mistake? There is almost nothing in the APP\Co..\Routes.php except :
$routes->setTranslateURIDashes(false);
$routes->set404Override();
$routes->setAutoRoute(true);

Thanks!