Preview:
<?php
ini_set('display_errors',1);
error_reporting(E_ALL);


Instead of:
$user_id = _POST['user_id'];
Or
$user_id = $POST['user_id'];

It should read:
$user_id = $_POST['user_id'];
downloadDownload PNG downloadDownload JPEG downloadDownload SVG

Tip: You can change the style, width & colours of the snippet with the inspect tool before clicking Download!

Click to optimize width for Twitter