How to disable IPN for a specific button

Question

We're running WPMUdev's Memberships plugin, which requires that the default IPN lister URL be set in one's PayPal profile (because even though the subscribe buttons include notify_url, without a default IPN listener set, apparently there's no way to get recurring payment cancellation messages) — and that all works just fine.

Trouble is, PayPal can't tell the difference between buttons generated by this plugin and manually generated buttons (eg one-off donation), and tries to send IPN messages to the plugin's listener, which gets completely confused because the expected metadata isn't sent with it. PayPal then retries the IPN until its limit is reached.

Is there some way to use notify_url (or some other HTML variable) to disable IPN messages for a specific button? Or will I have to write a null IPN listener that simply acknowledges IPN messages and drops them on the floor?

Answer 1

What @EdSF said is what I would recommend.

Setup an IPN listener that does nothing but return a 200 OK back to PayPal. It doesn't have to actually do anything.

Then set that URL as the value of notify_url in the button that you want to "disable".

This will way you won't end up with loops of IPNs from PayPal trying to hit a bogus URL that doesn't exist.

Answer 2

In the scenario I've described, it's evident that providing a null notify_url doesn't work (the default IPN listener URL is still used) therefore (unless a more experienced PayPal developer can indicate otherwise), and as @Andrew Angell said, it will be necessary to provide an IPN listener that simply acknowledges the IPN message (and maybe logs it, if desired).

Note that, as described in PayPal's documentation, it is not sufficient simply to reply with an HTTP 200 response; PayPal will continue to retry IPNs until the limit is exceeded or the configured listener responds with the appropriate positive acknowledgement described in that link.

There are any number of IPN listener templates available on the web, so that is one option, however here's another that has only just occurred to me:

There are one or two IPN multiplexor scripts floating around, for example, this one, though I haven't yet tried it so can't speak to its quality or suitability. But I'd guess that using a pre-existing multiplexor script would be the sensible thing to do because a) it deals with the problem I presented in my OP, and b) it provides a ready-made mechanism for dealing with other applications that make use of IPN, should the need arise.