According to PayPal’s documentation,
"When a customer makes a payment to you or a payment is reversed or refunded,
PayPal will post a notification to your server at the URL you specified."
You provide them with the page, e.g. www.my-site.com/process.php, and payment should post.
Handle that with
if ($_POST["payment"] != ""){
...your code to interact with your database
}
solved How to automaticly update some thing after user pay with paypal [closed]