Develop a paypal plugin for Invision Powerboard 4.0

I need an application that allows members to purchase a subscription to an item and it change their usergroup on the forum when they purchase. But also change it back if their subscription is canceled or not paid for on paypal. This will require paypal to communicate back with IPB. I do not know if this is possible anymore but they have a plugin for this application on the old IPB, I want to develop it for the new IPB 4.0 forum software. This is the old version that no longer works for the latest IPB 4.0 [login to view URL] You were able to add different subscriptions, prices, pick which group they went to, when the subscription would renew etc. Worked perfectly integrated with Paypal and their subscriptions.