Сокращение ссылок goo.gl

<?php
$id = $modx->resource->get('id');
$long_url = $modx->makeUrl($id,'','', "full");
$google_api_key = 'API_KEY';

function shorten($url,$key){
	$ch = curl_init(); 
	curl_setopt($ch, CURLOPT_URL, "https://www.googleapis.com/urlshortener/v1/url?key={$key}"); 
	curl_setopt($ch, CURLOPT_HTTPHEADER, array("Content-Type: application/json")); 
	curl_setopt($ch, CURLOPT_RETURNTRANSFER, true); 
	curl_setopt($ch, CURLOPT_POST, true); 
	curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode(array('longUrl' => $url))); 
	$result = curl_exec($ch);
 	$json = json_decode($result);
 	curl_close($ch);
 	return $json->id;
 }

$short_url = shorten($long_url,$google_api_key);
echo $short_url;