, Paypal , Paynal IPN. IPN- PayPal, : http://www.domain.com/ipn.php. PayPal, , ..
IPN Paypal :
https://www.paypal.com/ipn
Paypal , , . , , , userid = 100, username = Nickname registered_email=xxx@gmail.com. userid = 100 paypal. CUSTOM = 100.
ipn.php script, . , Paypal http://www.domain.com/ipn.php ( PayPal URL IPN). , ipn.php , , . CUSTOM ($ _POST ['custom']), 100 (userid). - , , , .
, . , PayPal, . , , , - . - .