Server-to-Server App using Google Drive not responses to APIs calls

Question

I'm working on a project where I have to make a server to server app with PHP.

The concept is : the company uploads bills to Google drive and the users use the website to retrieve their bills. First of all I didn't use a composer to the server because I have no permission to install. So I downloaded the libs and uploaded to server with ftp. Then I created a G Suite Google account and followed the instructions from their guide https://developers.google.com/api-client-library/php/auth/service-accounts.

The weird thing is if var_dump(service) after $results = $service->files , I see that the verification for the client has be done. When I try to use the api with $results = $service->files->listFiles($optParams); the page doesn't respond. Im really confused with this.

<?php
session_start();
require_once "vendor/autoload.php";
require 'init.php';

putenv('GOOGLE_APPLICATION_CREDENTIALS=service.json');

$client = getClient();
$service = new Google_Service_Drive($client);

function getClient() {
    $client = new Google_Client();
    $client->useApplicationDefaultCredentials();
    return $client;
}
 $optParams = array(
    'pageSize' => 5,
    'fields' => 'files(webViewLink, name , parents, id)'
);

$results = $service->files->listFiles($optParams);

Answer 1

Solved it. The problem was PHP version. I switched to 7.2 and seems to work perfect!