How to set up PayPal IPN notifications

Hi,

Well, I was doing okay with the setup, including PayPal APIs, etc. until I got to this: "To use PayPal Express Checkout or Pro you must manually turn on IPN notifications and enter your IPN url (http://earthwho.com/wp-admin/admin-ajax.php?action=psts_pypl_ipn) in your PayPal profile (you must also do this in your sandbox account when testing)."

I don't see a place to do that in my PayPal profile. Your help will be greatly appreciated.

Thanks,
Mac