Works like a charm

I’ve created an IPN listener in other php applications, but I’m not familiar with WordPress so it I was a bit lost when trying to create a place to catch the ipn within the functions.php file. This plugin makes it easy. It gives you a number of hooks (handlers?) to deal with various ipn types, but I prefer to use the catch-all handler:

add_action('paypal_ipn_for_wordpress_ipn_response_handler', 'process_IPN', 10, 1);
function process_IPN( $posted ) {...}