Phalcon\Mvc\Dispatcher\Exception: Frontend\Controllers\IndexController handler class cannot be loaded

<?php
 
require_once __DIR__ . '/../common/lib/global-functions.php';
 
class Bootstrap
{
    private $app;
 
    public function __construct()
    {
        // Dependency Injector
        $di = new \Phalcon\DI\FactoryDefault();
 
        // Configuration
        $config = loadConfigFile('config');
        $databaseCredentials = $config->sensitive->database;
        unset($config->sensitive);
        $di->setShared('config', $config);
 
        // 301 Redirect if /public/index.php
        $currentUrl = getCurrentUrl();
        if (strpos($currentUrl, 'public/index.php') !== false) {
            return $di->getResponse()->redirect($config->site->url, true, 301)->send();
        }
 
        // 301 Redirect if /public/ - Replace only the first occurance of /public/
        $currentPath = str_replace($config->site->url, '', $currentUrl);
        if (substr($currentPath, 0, 6) == 'public') {
            $needle = '/public/';
            $redirect = substr_replace($currentUrl, '/', strpos($currentUrl, $needle), strlen($needle));
            return $di->getResponse()->redirect($redirect, true, 301)->send();
        }
 
        // Router
        $di->setShared('router', function() use ($di, $config) {
            $router = new \Phalcon\Mvc\Router();
 
            $uri = $di->getRequest()->getURI();
            $uriHint = substr($uri, 0, 8);
 
            $module = 'Frontend';
            if ($uriHint == '/api/v1/') {
                $module = 'Api';
            }
 
            $router->setDefaultModule(strtolower($module));
            $router->setDefaultNamespace($module . '\Controllers');
            $router->setDefaultController('index');
            $router->setDefaultAction('index');
            $router->removeExtraSlashes(true);
            require_once $config->site->path->configs . 'routes.php';
            return $router;
        });
 
        // Crypt
        $di->setShared('crypt', function () use ($config) {
            $crypt = new \Phalcon\Crypt();
            $crypt->setKey('i$4^&/:%2@k%0ROQ<@{(e=*!<2u|rI~4');
            return $crypt;
        });
 
        // URL component
        $di->setShared('url', function() use ($config) {
            $url = new \Phalcon\Url();
            $url->setBaseUri($config->site->url);
            $url->setStaticBaseUri($config->site->staticUrl);
            return $url;
        });
 
        if (IS_CLI_EXECUTE === false) {
            $di->set('session', function () use ($config) {
                $session = new \Phalcon\Session\Manager;
                $adapter = new \Phalcon\Session\Adapter\Stream([
                    // 'uniqueId' => 'drooble-' . $config->module,
                    'savePath' => $config->site->path->cache . 'sessions/'
                ]);
                $session->setAdapter($adapter);
                $session->start();
                return $session;
            });
        }
 
        // Cache
        $di->setShared('cache', function() use ($config) {
            $serializerFactory = new \Phalcon\Storage\SerializerFactory();
            $adapter = new \Phalcon\Cache\Adapter\Stream($serializerFactory, [
                'defaultSerializer' => 'Json',
                'storageDir' => $config->site->path->cache . 'site',
                'lifetime' => 172800, // 2d
                'serializer' => new \Phalcon\Storage\Serializer\Json()
            ]);
            return new \Phalcon\Cache($adapter);
        });
 
        // Database connection. Use set() if Transactions are needed
        if ($databaseCredentials->DATABASE_DISABLED !== true) {
            $di->setShared('db', function() use ($databaseCredentials) {
                return new \Phalcon\Db\Adapter\Pdo\Mysql([
                    'host' => $databaseCredentials->host,
                    'username' => $databaseCredentials->username,
                    'password' => $databaseCredentials->password,
                    'dbname' => $databaseCredentials->name,
                    // 'charset' => 'utf8',
                    'options'  => [
                        \PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES utf8',
                        \PDO::ATTR_PERSISTENT => true,
                        \PDO::ATTR_STRINGIFY_FETCHES => false
                    ]
                ]);
            });
        }
 
        $this->app = new \Phalcon\Mvc\Application();
        $this->app->setDI($di);
    }
 
    public function run()
    {
        $modules = [
            'frontend' => [
                'className' => 'Frontend\Module',
                'path' => __DIR__ .'/frontend/Module.php'
            ],
        ];
 
        // Is there an API?
        $uri = $this->app->request->getURI();
        if ($this->app->config->dev->hasApi === true AND substr($uri, 0, 5) == '/api/') {
            // Extract api version from url: /api/v1/robots...
            $parts = array_filter(explode('/', $uri));
 
            // Save API version
            $this->app->config->apiVersion = $parts[2];
 
            // Add to modules
            $modules['api'] = [
                'className' => 'Api\Module',
                'path' => __DIR__ .'/api/'. $this->app->config->apiVersion .'/Module.php'
            ];
        }
 
        // Register application modules
        $this->app->registerModules($modules);
        echo $this->app->handle($uri)->getContent();
    }
 
    public function getApp()
    {
        return $this->app;
    }
}

<?php
    try {
        define('DEV', in_array($_SERVER['REMOTE_ADDR'], ['77.70.108.105', '::1']));
        define('IS_CLI_EXECUTE', false);
        $root = str_replace('\\', '/', dirname(dirname(__FILE__))) . '/';
        require_once $root . 'apps/Bootstrap.php';
        $bootstrap = new Bootstrap();
 
        // Listen for all notices, warnings and exceptions in Dev mode
        if ($bootstrap->getApp()->config->debug === true) {
            error_reporting(E_ALL);
            ini_set('display_errors', 1);
 
            $debug = new \Phalcon\Debug();
            $debug->listenLowSeverity();
        } else {
            error_reporting(0);
        }
 
        $isWebpSupported = (isset($_SERVER['HTTP_ACCEPT']) && ($_SERVER['HTTP_ACCEPT'] == '*/*' OR strpos($_SERVER['HTTP_ACCEPT'], 'image/webp') !== false));
        define('WEBP_SUPPORT', $isWebpSupported);
 
        // Run
        $bootstrap->run();
    } catch (\Exception $e) {
        if ($bootstrap->getApp()->config->debug === true) {
            $debug = new \Phalcon\Debug();
            die($debug->listen()->onUncaughtException($e));
        } else {
            // Log the error
            // $logFile = $bootstrap->getApp()->config->site->path->logs . 'errors/error-500_'. date('YmdHis') .'_'. mt_rand(1, 1000000) .'.txt';
            // file_put_contents($logFile, var_export($e, true));
            error_log($e);
 
            // Output for user
            header('HTTP/1.1 500 Internal Server Error');
            die(file_get_contents('../apps/frontend/views/_layouts/error-500.phtml'));
        }
    }