If payment is made, allow access to another site

I have a site that I am running WooCommerce plugins on. I have a plugin that allows new users to automatically become a subscriber of any site I allow called (Multisite User Management). Now I want people to purchase something from my site (shop.mysite.com) and when payment is processed by paypal, they are allowed to become a subscriber of (support.mysite.com)

Anyone know of a good trick to do this?