Phalcon\Application\Exception: Module 'Site' isn't registered in the application container

<?php
 
namespace Backend;
 
use Phalcon\DiInterface;
use Phalcon\Mvc\Application;
use Phalcon\Mvc\Router;
 
class App
{
  /**
   * @var \Phalcon\DiInterface
   */
  private $_di;
 
  /**
   * @var \Phalcon\Mvc\Application
   */
  private $_application;
 
  /**
   * @var \Phalcon\Config
   */
  private $_config;
 
  /**
   * App constructor.
   *
   * @param $_dependencyInjector
   */
  public function __construct(DiInterface $_dependencyInjector)
  {
    $this->_di = $_dependencyInjector;
 
    $this->_config = $_dependencyInjector->get('config');
 
    $this->createPhalconApplication();
    $this->registerRoutes();
    $this->registerServices();
  }
 
  /**
   * @return string
   */
  public function getContent()
  {
    return $this->_application->handle()->getContent();
  }
 
  /**
   * @return \Phalcon\Mvc\Application
   */
  private function createPhalconApplication()
  {
    /**
     * Приложение
     */
    $this->_application = new Application($this->_di);
 
    /**
     * Регистрация установленных модулей
     */
    $this->_application->registerModules([
      'admin' => [
        'className' => 'Backend\Modules\Admin\Module',
      ],
      'site'  => [
        'className' => 'Backend\Modules\Site\Module',
      ],
      'api'   => [
        'className' => 'Backend\Modules\API\Module',
      ],
    ]);
 
    return $this->_application;
  }
 
  private function registerRoutes()
  {
    /**
     * Registering a router
     */
    $this->_di->set('router', function () {
      $router = new Router(false);
 
      $router
        ->removeExtraSlashes(true)
        ->mount(new \Backend\Modules\Site\Routes())
        ->mount(new \Backend\Modules\Admin\Routes())
        ->mount(new \Backend\Modules\API\Routes());
 
      $router->notFound([
        'module'     => 'Site',
        'controller' => 'Index',
        'action'     => 'Route404',
      ]);
 
      return $router;
    });
  }
 
  private function registerServices()
  {
    $di = $this->_di;
 
    $di->set('redisConnection', function () {
 
      $config = $this->get('config');
 
      $Redis = new \Redis();
      $Redis->connect($config->redis->connection->host);
 
      return $Redis;
    });
  }
}

<?php
 
define('BASE_DIR', dirname(__DIR__));
 
ini_set('memory_limit', '-1');
 
//Временная зона
ini_set('date.timezone', 'Europe/Minsk');
 
if ( !defined('DEBUG') ) {
  error_reporting(0);
  ini_set('display_errors', '0');
}
 
/**
 * Read loader
 */
include __DIR__ . '/loader.php';
 
/**
 * Read services
 */
include __DIR__ . '/services.php';
 
$app = new \Backend\App($di);
 
echo $app->getContent();

<?php
 
define('DEBUG', true);
 
error_reporting(E_ALL);
ini_set('display_errors', 1);
 
(new Phalcon\Debug())->listen();
 
include dirname(__DIR__) . '/config/app.php';