标准应用引擎上的Kreait Firebase PHP

Question

I've been trying to resolve why my script isn't called.

I'm using PHP Google Standard App Engine. I have a Users class with the following construction/members:

<?php

require_once __DIR__ . '/vendor/autoload.php';

use Kreait\Firebase\Factory;

class Users {

//db
protected $database;
protected $dbname = 'users';
private $ref; 

<member_variables>

public function __construct(<arguments>){

    //firebase sync
    $firebase = (new Factory())->create();
    $this->database = $firebase->getDatabase();
    $this->ref = $this->database->getReference();

    <member assignment>


}

My code stops executing when I call this class. Is there something I'm doing wrong here?

Thanks :)