Affiliate program and Paypal problems

This is the last step in setting up my affiliates program. Can anyone tell me where in zen I will find what this step is asking for?

(3) Edit the notify_url field in your Paypal button form code. You must add the following line to the end of your notify URL.
?custom=<?php echo "$_SERVER[REMOTE_ADDR]"; ?>
An example complete notify_url field would appear like this :
<INPUT TYPE="hidden" NAME="notify_url" VALUE="http://www.yourdomain.com/ipnscript.php?custom=<?php echo $_SERVER[REMOTE_ADDR]; ?>">

I have looked for hours,
Thanks,
Amy b

Hi Amy remember im new . but have you tryed in the admin panel
module/paypal IPN then edit or instal and add them at the bottom of the edit panel.
Hope thats some good Amy :)

Nope, that didn't do it..

I need to find the notify Url for paypal so I can edit it. Does anyone know where it is located?

Amy B