Jobs and Experts: How to setup the Credits

Hi I hope you are fine

We want to setup the credit system for Jobs and Experts but could not find a good and working tutorial until now.

What are the necessary steps if paypal will be the payment gateway and users should purchase credits which they can use on the jobs and expert system.

As the credit systems are different and not compatible between the wpmudev plugins we also would like to know what would be actually the best way to get the credit system up and running for all plugins.

Or - and this would be another option we have would be membership similar to wpmudev where people by a membership and than can i.e. setup unlimited jobs post items create a website but perhaps would need to pay also for additional features. What would be the best approach.

Our base theme is using paid membership pro

Pro-sites has its own way with a different way on how to setup paypal than pmp

Ideas and a tutorial/walkthrough on how to setup the creditsystem in jobs and experts are very welcome