return path for Paypal IPN URL

Hi - I'm using a 3rd-party paypal IPN forwarding setup to allow using paypal on multiple domains

I'm a little lost trying to determine what the redirect (return) URL would be for Pro Site transactions

is it /wp-admin/admin-ajax.php?action=psts_pypl_ipn

also, the redirect relies on filtering the "product name", so what's the name of a Pro Site product (as sent to paypal for payment)?