How to create a Paid Plugin Store

The info page for Pretty Plugins says:

"Pretty Plugins is an essential tool for the network owner. Providing centralized control and configuration of every site’s Plugins page. Combine with Pro Sites to create an awesome paid plugin store."

What I'd like to know is: how to create a "paid plugin store"? It sounds like I can offer activation on a per plugin basis. How do I do that?

https://premium.wpmudev.org/project/pretty-plugins/

I posted this question before but did not get an appropriate response, just another question. I'm hoping the next person can actually offer support, since I did pay for support.

Thank you.