index by default not load on multi module project

Hi!, i have a little problem,

i configured my project, with multi module structure, when i try to access to: https://feedback/public/index the error page load, but if i try with: https://feedback/public/index/index the real page load, so, what is the problem? this is my bootstrap conf:

<?php

error_reporting(E_ALL);

try {
        define('SITE_DOMAIN', $_SERVER['HTTP_HOST']);

    /**
     * Read the configuration
     */
    $config = include(__DIR__.'/../app/config/'.SITE_DOMAIN.'_db.php');

    /**
     * The FactoryDefault Dependency Injector automatically register the right services providing a full stack framework
     */
    $di = new \Phalcon\DI\FactoryDefault();

    /**
     * The URL component is used to generate all kind of urls in the application
     */
    $di->set('url', function() use ($config) {
        $url = new \Phalcon\Mvc\Url();
        $url->setBaseUri($config->application->baseUri);
        return $url;
    });

        /**
     * Database connection is created based in the parameters defined in the configuration file
     */
    $di->set('db', function() use ($config) {
        return new \Phalcon\Db\Adapter\Pdo\Mysql(array(
            "host" => $config->database->host,
            "username" => $config->database->username,
            "password" => $config->database->password,
            "dbname" => $config->database->name
        ));
    });

    /**
     * If the configuration specify the use of metadata adapter use it or use memory otherwise
     */
    $di->set('modelsMetadata', function() use ($config) {
        if (isset($config->models->metadata)) {
            $metadataAdapter = 'Phalcon\Mvc\Model\Metadata\\'.$config->models->metadata->adapter;
            return new $metadataAdapter();
        } else {
            return new \Phalcon\Mvc\Model\Metadata\Memory();
        }
    });

    /**
     * Start the session the first time some component request the session service
     */
    $di->set('session', function() {
        $session = new \Phalcon\Session\Adapter\Files();
        $session->start();
        return $session;
    });

        //Specify routes for modules
        $di->set('router', function () {
            $router = new \Phalcon\Mvc\Router(false);
            $router->setDefaultModule("backend");
            $router->setDefaultAction('index');
            $router->notFound(array(
            'module' => 'backend',
            'controller' => 'error',
            'action' => 'index'
            ));
           $router->add('/:module/:controller/:action/:params', array(
            'module' => 1,
            'controller' => 2,
            'action' => 3,
            'params' => 4
            ));            
            return $router;
        });
    /**
     * Handle the request
     */
    $application = new \Phalcon\Mvc\Application();
    $application->setDI($di);
        // Register the installed modules
        $application->registerModules(
            array(
                'public' => array(
                    'className' => 'Frontend\Module',
                    'path'      => '../app/frontend/Module.php',
                ),
                'backend'  => array(
                    'className' => 'Backend\Module',
                    'path'      => '../app/backend/Module.php',
                )
            )
        );

    echo $application->handle()->getContent();

} catch (Phalcon\Exception $e) {
    echo $e->getMessage();
} catch (PDOException $e){
    echo $e->getMessage();
}

Any Help please!