Well, it turns out that I already asked this question here on this forum two years ago. But the question persists because the inconsistencies in the WP eCommerce documentation and user-interface hints have still not been updated or corrected.
In my original post a plugin author responded that I should NOT enable IPN in my PayPal account settings:
Normally you don`t need to enable IPN in your Paypal account.
You must enable it in the Payments setup page in your store for Paypal Payments Standard.
Once you enable it for the gateway ( under store -> Payments ) then WPEC will send a notify_url field to which paypal will send post data back.
If IPN is not set in your Paypal account BUT notify_url is sent to paypal with a order then the data is sent to the notify_url we send.
…
You should disable IPN in your account or remove the url.
As in the paypal comments IF the Account has IPN url set it will use that and not the IPN url that WP e-Commerce sends automatically with the purchase.
In that same post, myself and others noted that this advice is missing from the WP eCommerce documentation (the URL of which has changed, and is now located here). We asked that the documentation be updated — but it hasn’t been. We also noted that this advise contradicts the help text provided in the WP eCommerce admin area, and two years later the help text still contradicts this advise. (It recommends enabling IPN in your PayPal settings.)
I’d still like to know if I can “enable” IPN in the PayPal settings page, and leave the URL field blank? But even that seems like it might be wrong…
So more importantly, I’d like to know if WP eCommerce does in fact provide a “listener” page as described in this PayPal IPN Documentation page? According to that page, there are other instances where PayPal might use the IPN feature, besides an immediate response to the payment being made. For example, if the customer subsequently cancels their credit card payment, PayPal would send a message to the “listener” located at the URL we are asked to provide on the PayPal IPN settings page. But if we disable IPN in our PayPal settings, or leave the “URL” field blank, we cannot be notified. So my question now remains: does WP eCommerce provide a “listener” page as recommended by PayPal (in which case we need to provide it’s URL), or not? If so, what should that URL be?
Thanks!