Error: Class 'Facebook\FacebookSession' not found with the facebook PHP SDK

I am having a hard time with facebook's SDK documentation. I downloaded the SDK from Github and added it into my PHP project.

Here is the file system:

   ├── Facebook
   │   ├── FacebookAuthorizationException.php
   │   ├── FacebookCanvasLoginHelper.php
   │   ├── FacebookClientException.php
   │   ├── FacebookJavaScriptLoginHelper.php
   │   ├── FacebookOtherException.php
   │   ├── FacebookPermissionException.php
   │   ├── FacebookRedirectLoginHelper.php
   │   ├── FacebookRequest.php
   │   ├── FacebookRequestException.php
   │   ├── FacebookResponse.php
   │   ├── FacebookSDKException.php
   │   ├── FacebookServerException.php
   │   ├── FacebookSession.php
   │   ├── FacebookThrottleException.php
   │   ├── GraphLocation.php
   │   ├── GraphObject.php
   │   ├── GraphSessionInfo.php
   │   ├── GraphUser.php
   │   └── fb_ca_chain_bundle.crt
   └── test.php

here is my code so far:

use Facebook\FacebookSession;
use Facebook\FacebookRequest;
use Facebook\GraphUser;
use Facebook\FacebookRequestException;

FacebookSession::setDefaultApplication('*******','******');

$helper = new FacebookRedirectLoginHelper('http://isgeek.eu/fb/FaRepost/return.php');
$loginUrl = $helper->getLoginUrl();
// Use the login url on a link or button to redirect to Facebook for authentication

I get this error

Fatal error: Class 'Facebook\FacebookSession' not found in /homepages/2/d184071366/htdocs/isgeek/fb/FaRepost/test.php on line 9

At updated my PHP version, so the issue does not comme from here. It seems like the PHP files are not found. I read this question (Facebook SDK v4 for PHP Minimal Example) but it does not help.

Where does this comme from?

I found the solution here

I did not code in php for some time now and things have changed. use Facebook\FacebookSession; is not enough. You need to add a require_once too.

require_once 'Facebook/FacebookSession.php';