We are having a problem with IPN Notifications. We are receiving the PayPal Instant Payment Notification Warning emails when we receive a payment outside of our online store. The IPN URL works fine for store purchase, but fails when someone pays using a PayPal generated invoice. This makes sense, of course, because the store URL is not expecting a callback and refuses it when it comes from an invoice. Is there a way to set the IPN to ONLY respond to store purchases? Or at least turn it off for PayPal invoicing?