today i would ask you if someone know how Check if the user has really payed and then if he has really payed execute some mssql+script
for be precise if he has really payed i would execute this query via php: (UPDATE members SET Premium='1' WHERE membername="'.$membername.'"")
You can check this PHP example from paypal site:
https://cms.paypal.com/cms_content/US/en_US/files/developer/IPN_PHP_41.txt
if (strcmp ($res, "VERIFIED") == 0) {
// Your code
}
You can implement this using PayPal's Instant Payment Notification (IPN). However, it's important to understand that when the user comes back to your website from paying at PayPal, that does not mean the payment has gone through yet. The IPN could happen before they get back to your site or sometime later. You can even accept eCheck payments which can take quite a while to be a completed payment.
Therefore, your IPN listener script would wait for the completed payment, update the user's membership, and then send them an email with a link to login as a premium member.
The whole process is explained in this tutorial with example code: PayPal IPN with PHP