I have a client -- http://apluslongevity.com/ -- who uses Gravity Forms with the Paypal Add on. The paypal add on requires you to input an IPN URL that Gravity Form provides. This feature allows PayPal to notify Gravity Forms when a transaction has been processed in Paypal. This works fine. The problem is that we need Paypal to also notify MailChimp when a transaction occurs. MailChimp provides an IPN URL to enter, but PayPal only provides one place to enter an IPN URL. And that spot is currently taken up by the Gravity Forms IPN URL. I need you to find a way for Paypal to notify both services. A solution may be provided here, but I am not a programmer, so I don't want to attempt it: http://www.geekality.net/2011/05/28/php-tutorial-paypal-instant-payment-notification-ipn/