UPDATE 1:
According to this tutorial on Using PayPal\'s Instant Payment Notification with PHP, PayPal cannot access locally hosted websites unless c
To use IPN your localhost has to be accessed from the web. One solution that definitly works is to use a virtual Machine, install VPN-Server, connect your Clinet via VPN and manage virtual host to redirect to your local IP-adress. That way, if you turn on VPN your server can be accessed from outside and IPN can be sent.