private function request($query, $variables, $headers)
    {

        $ch = curl_init();

        curl_setopt($ch, CURLOPT_URL, $this->url);
        curl_setopt($ch, CURLOPT_HEADER, 0);
        curl_setopt($ch, CURLOPT_POST, 1);
        curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode(['query' => $query, 'variables' => $variables]));
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
        curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0);
        curl_setopt($ch, CURLOPT_HTTPHEADER, array_merge($headers, [
            "X-Token: {$this->token}",
            "Content-Type: application/json;charset=utf-8"
        ]));
        $output = curl_exec($ch);

        curl_close($ch);

        return $output;
    }