Response object not working

Phalcon 2.0.13 is not supported, but it will still work nicely with PHP 5.6.x. Next, your problem might be with how you bootstrap your app, and especially PATHS.

The best is to post here your full bootstrap (i.e. index.php), and your services definition.

P.S. Which web server you run? Apache or Nginx?

Ok, thanks for your response.

I initially downloaded Phalcon 3 and PHP 7.0, but because a friend that worked on the project was running the versions mentioned above, I installed the same versions as him. Are newer versions of both Phalcon and PHP backwards compatible?

I'm running Apache, I'll post the code for the bootstrap

root/public/index.php

<?php

use Phalcon\Mvc\Application;

define('APP_PATH', realpath('..'));

try {

    $config = require APP_PATH . "/config/config.php";

    /**
     * Include services
     */
    require APP_PATH . '/config/services.php';

    /**
     * Handle the request
     */
    $application = new Application($di);

    /**
     * Include modules
     */
    require APP_PATH . '/config/modules.php';

    // Handle the application:
    echo $application->handle()->getContent();
} 
catch (\Exception $e) {
    echo $e->getMessage() . '<br>';
    echo '<pre>' . $e->getTraceAsString() . '</pre>';
}

root/config/config.php

<?php

return new \Phalcon\Config(array(
    'database' => array(
        ...
    ),
    'application' => array(
        'controllersDir' => __DIR__ . '/../controllers/',
        'modelsDir'      => __DIR__ . '/../models/',
        'migrationsDir'  => __DIR__ . '/../migrations/',
        'viewsDir'       => __DIR__ . '/../views/',
        'baseUri'        => '/',
        'cacheDir'       => APP_PATH . '/cache/',
    )
));

root/config/services.php

<?php
/**
 * Services are globally registered in this file
 *
 * @var \Phalcon\Config $config
 */

use Phalcon\Loader;
use Phalcon\Mvc\Router;
use Phalcon\Mvc\Url as UrlResolver;
use Phalcon\Di\FactoryDefault;
use Phalcon\Session\Adapter\Files as SessionAdapter;
use Phalcon\Mvc\Model\Metadata\Memory as MetaDataAdapter;
use Phalcon\Mvc\View;
use Phalcon\Mvc\View\Engine\Volt as VoltEngine;
use Phalcon\Flash\Direct as FlashDirect;
use Phalcon\Flash\Session as FlashSession;

/**
 * The FactoryDefault Dependency Injector automatically registers the right services to provide a full stack framework
 */
$di = new FactoryDefault();

/**
 * Create a loader to register all files.
 */
$loader = new Loader();
$loader->registerNamespaces(array(
    'Apps' => APP_PATH . '/Apps/',
));
$loader->register();

/**
 * Registering a router
 */
$di->setShared('router', function () {
    $useSlugExtension = true;
    $router = new \Apps\Source\Plugins\Routing\Router($useSlugExtension);
    // $router = new \Apps\Source\Plugins\Routing\Router();

    $router->setDefaultModule('frontend');
    $router->setDefaultNamespace('\Apps\Modules\Frontend\Controllers');

    return $router;
});

/**
 * The URL component is used to generate all kinds of URLs in the application
 */
$di->setShared('url', function () use ($config) {
    $url = new UrlResolver();
    $url->setBaseUri($config->application->baseUri);

    return $url;
});

/**
 * Setting up the view component
 */
$di->setShared('view', function () use ($config) {

    $view = new View();

    $view->setViewsDir($config->application->viewsDir);

    $view->registerEngines(array(
        '.volt' => function ($view, $di) use ($config) {

            $volt = new \Phalcon\Mvc\View\Engine\Volt($view, $di);

            $volt->setOptions(array(
                'compiledPath' => $config->application->cacheDir,
                'compiledSeparator' => '_'
            ));

            return $volt;
        },
        '.phtml' => function ($view, $di) use ($config) {

            $volt = new \Phalcon\Mvc\View\Engine\Volt($view, $di);

            $volt->setOptions(array(
                'compiledPath' => $config->application->cacheDir,
                'compiledSeparator' => '_'
            ));
            // Add functions to the compiler:
            $volt->getCompiler()->addFunction(
                'in_array', 'in_array'
            );

            return $volt;
        }
    ));

    return $view;
});

/**
 * Database connection is created based in the parameters defined in the configuration file
 */
$di->setShared('db', function () use ($config) {
    $dbConfig = $config->database->toArray();
    $adapter = $dbConfig['adapter'];
    unset($dbConfig['adapter']);

    $class = 'Phalcon\Db\Adapter\Pdo\\' . $adapter;

    return new $class($dbConfig);
});

/**
 * If the configuration specify the use of metadata adapter use it or use memory otherwise
 */
$di->setShared('modelsMetadata', function () {
    return new MetaDataAdapter();
});

/**
 * Starts the session the first time some component requests the session service
 */
$di->setShared('session', function () {
    $session = new SessionAdapter();
    $session->start();

    return $session;
});

/**
 * Add authentication management
 */
$di->setShared('auth', function() use ($di) {
    $session = $di->get('session');
    $auth = \Apps\Source\Components\AuthManager::getInstance($session);
    return $auth;
});

/**
 * Date manager
 */
$di->setShared('date', function(){
    return new \Apps\Source\Plugins\Date\Manager();
});

/**
 * Register the direct flash service with the Twitter Bootstrap classes
 */
$di->set('flash', function () {
    return new FlashDirect(
        array(
            'error'   => 'alert alert-danger',
            'success' => 'alert alert-success',
            'notice'  => 'alert alert-info',
            'warning' => 'alert alert-warning'
        )
    );
});

/**
 * Register the session flash service with the Twitter Bootstrap classes
 */
$di->set('flashSession', function () {
    return new FlashSession(
        array(
            'error'   => 'alert alert-danger',
            'success' => 'alert alert-success',
            'notice'  => 'alert alert-info',
            'warning' => 'alert alert-warning'
        )
    );
});

/**
 * Set the default namespace for dispatcher
 */
$di->setShared('dispatcher', function() use ($di) {
    $eventsManager = new \Phalcon\Events\Manager();
    $eventsManager->attach("dispatch:beforeException", function($event, $dispatcher, $exception) {
        //Handle 404 exceptions
        if ($exception instanceof \Phalcon\Mvc\Dispatcher\Exception) {
            $dispatcher->forward(array(
                'namespace' => 'Apps\Modules\Frontend\Controllers',
                'module' => 'frontend',
                'controller' => 'error',
                'action' => 'show404'
            ));
            return false;
        }
    });
    $dispatcher = new \Phalcon\Mvc\Dispatcher();

    //Bind the EventsManager to the dispatcher
    $dispatcher->setEventsManager($eventsManager);

    return $dispatcher;
});