Thanks Maeve. One more question on that: which URL do I need to save in my PayPal account as Notification URL? Is it
a) http://websitename.com/wp-content/plugins/paypal-responder/ipn.php
or
b) http://websitename.com/?AngellEYE_Paypal_Ipn_For_Wordpress&action=ipn_handler
the second one (b) is generated from a WP plugin called PayPal IPN.