Sorry for the delay jumping in here. It sounds like what’s happening is ContactForm is overriding the IPN URL using the Notify parameter in its payment request. You would need to disable this so that the profile URL (our plugin’s URL) gets used instead.
When you do this, of course, that means whatever ContactForm is doing with its own IPN would not trigger, so if it’s marking payments completed or anything like that then that would break.
What you could do that point, though, is forward the IPN data from our plugin to the URL that ContactForm is trying to use. This way whatever you’re doing with our plugin would trigger, and the ContactForm script would also trigger.
You could do this manually by building in a function that does it, or we also have a premium extension plugin that was built specifically for this sort of thing. It will allow you to setup as many additional URLs as you need to forward IPN data to.
Let me know if you have any questions about any of that. Thanks!