PostHog namespace issue – PHP

I installed PostHog in my PHP codebase, and trying to use it by following the tutorial in this link (https://posthog.com/docs/integrate/server/php).

I am attempting to call PostHog::init function as a following:

       PostHog::init($apikey,
        array('host' => $baseUrl,
            "debug" => true)
    );

But I am getting error in this line PostHog::init, the error says

"Attempted to load class PostHog" from the global namespace. Did you forget a "use" statement?"

In fact, I am already using the "use" as following "use PostHogPostHog;", but I am still getting this error. I can confrim that the Posthog library is intall becuase I can read the classess in Poshog library from my codebase.

This is more info about my app:

• I use Symfony framework 5 and the app is deployed in docker. I use PHP 7.4 and posthog/posthog-php": "2.1.1".

• I checked the vendor folder and PostHog is there (see photo attached)

• I implemented service call PosthogHandler where I use PostHog functions (like init, capture and etc). I am calling functions’ services from controller. But the issue is that the error appear in the PosthogHandler constructor in line PostHog::init, at PostHog initialisation stage. This is my PosthogHandler service class:

<?php
    declare(strict_types=1);
    
    namespace AppPosthogs;
    
    use PostHogPostHog;
    use AppUserUser;
    
    class PosthogHandler
    {
        public function __construct($env, string $key, string $baseUrl)
        {
    
            PostHog::init($key,
                array('host' => $baseUrl,
                    "debug" => true)
            );
    
        }
    
        public function addEvent(string $eventName, User $user){
    
            PostHog::capture(array(
                'distinctId' => $user->getId()->id(),
                'event' => $eventName
            ));
        }
    
    }

Any help, why I am getting above error?