Google Calendar API fetchAccessTokenWithAuthCode not working - php

Question

I am stucked 3 days ago with Google Calendar API, I am new in Google API.
First of all I want to get events from users calendar.
I went through on the install process a few times, but my code always stop at fetchAccessTokenWithAuthCode function.
Probably I miss something really obvious, but I can't figure out what is wrong.
In web root I created a new folder for testing with 2 basic file from Google install site.
My php files:
index.php:
<?php
require_once 'path/googleapi/vendor/autoload.php';
session_start();
$client = new Google_Client();
$client->setAuthConfig('path/googleapi/credentials.json');
$client->addScope(Google_Service_Calendar::CALENDAR_READONLY);
$client->setRedirectUri('https://site/google/oauth2callback.php');
$client->setAccessType('offline');
$client->setPrompt("consent");
$client->setIncludeGrantedScopes(true);
$auth_url = $client->createAuthUrl();
var_dump($auth_url);
if (isset($_SESSION['access_token']) && $_SESSION['access_token']) {
var_dump($_SESSION);
} else {
header('Location: ' . filter_var($auth_url, FILTER_SANITIZE_URL));
}
?>
oauth2callback.php:
<?php
require_once 'path/googleapi/vendor/autoload.php';
session_start();
$client = new Google_Client();
$client->setAuthConfig('path/googleapi/credentials.json');
$client->setRedirectUri('https://site/google/oauth2callback.php');
$client->addScope(Google_Service_Calendar::CALENDAR_READONLY);
$client->setAccessType("offline");
if (! isset($_GET['code'])) {
$auth_url = $client->createAuthUrl();
header('Location: ' . filter_var($auth_url, FILTER_SANITIZE_URL));
} else {
var_dump($_GET['code']);
$token = $client->fetchAccessTokenWithAuthCode($_GET['code']);
echo "<br>token:<br>";
var_dump($token);
$_SESSION['access_token'] = $client->getAccessToken();
$redirect_uri = 'https://site/google/';
header('Location: ' . filter_var($redirect_uri, FILTER_SANITIZE_URL));
}
?>
I got redirected to Google's site, once I grant permission I am redirected to the oauth2callback.php
In oauth2callback.php I can see the var_dump output for the code, but no further output, which means no response from fetchAccessTokenWithAuthCode function.
Any help is appreciated