Question about Paypal IPN script

I used the default paypal script I found online for my website. For the most part it processes recurring subscriptions just fine. Occasionally the following IF statement is executed and I’m not sure why. Can someone explain this?


if (strcmp ($res, “INVALID”) == 0) {


Paypal returns INVALID to the paypalipn script if the values passed to it by the script are not ones that it has seen previously. This is how it prevents the IPN script completing a non existent payment if the IPN script is called directly rather than being called from Paypal.

So is it nothing to worry about when this takes place? Is this likely from a googlebot or other indexing spider hitting the page? Wait, no that can’t be it, because I track the IP address when the IPN script is run, and it always belongs to paypal when this INVALID situation occurs. So why is paypal executing my script in an invalid setting? Any info you can provide would really be appreciated!!!

felgall, are you still there?