Facebook SDK V4 get name - php

Question

For example, I want to retrieve my name using Facebook PHP SDK 4.
For that I use this code
<?php
require_once( 'Facebook/HttpClients/FacebookHttpable.php' );
require_once( 'Facebook/HttpClients/FacebookCurl.php' );
require_once( 'Facebook/HttpClients/FacebookCurlHttpClient.php' );
require_once( 'Facebook/Entities/AccessToken.php' );
require_once( 'Facebook/Entities/SignedRequest.php' );
require_once( 'Facebook/FacebookSession.php' );
require_once( 'Facebook/FacebookRedirectLoginHelper.php' );
require_once( 'Facebook/FacebookRequest.php' );
require_once( 'Facebook/FacebookResponse.php' );
require_once( 'Facebook/FacebookSDKException.php' );
require_once( 'Facebook/FacebookRequestException.php' );
require_once( 'Facebook/FacebookOtherException.php' );
require_once( 'Facebook/FacebookAuthorizationException.php' );
require_once( 'Facebook/GraphObject.php' );
require_once( 'Facebook/GraphSessionInfo.php' );
use Facebook\HttpClients\FacebookHttpable;
use Facebook\HttpClients\FacebookCurl;
use Facebook\HttpClients\FacebookCurlHttpClient;
use Facebook\Entities\AccessToken;
use Facebook\Entities\SignedRequest;
use Facebook\FacebookSession;
use Facebook\FacebookRedirectLoginHelper;
use Facebook\FacebookRequest;
use Facebook\FacebookResponse;
use Facebook\FacebookSDKException;
use Facebook\FacebookRequestException;
use Facebook\FacebookOtherException;
use Facebook\FacebookAuthorizationException;
use Facebook\GraphObject;
use Facebook\GraphSessionInfo;
FacebookSession::setDefaultApplication('app_id', 'app_secret');
// If you already have a valid access token:
$session = new FacebookSession('access token');
// To validate the session:
try {
$session->validate();
} catch (FacebookRequestException $ex) {
// Session not valid, Graph API returned an exception with the reason.
echo $ex->getMessage();
} catch (\Exception $ex) {
// Graph API returned info, but it may mismatch the current app or have expired.
echo $ex->getMessage();
}
try {
$response = (new FacebookRequest($session, 'GET', '/me'))->execute();
$object = $response->getGraphObject();
echo $object->getProperty('name');
} catch (FacebookRequestException $ex) {
echo $ex->getMessage();
} catch (\Exception $ex) {
echo $ex->getMessage();
}
?>
I get my access token from this link :
https://graph.facebook.com/oauth/access_token?client_id={app-id} &client_secret={app-secret}&grant_type=client_credentials
When I execute the code I get this error :
An active access token must be used to query information about the
current user.
What i'm doing wrong ? Thanks