Ask HN: Examples of default business processes for prepaid/postpaid orders?

I'm currently creating a statemachine driven checkout process for my startup. When I started to draw a business process for the events that can happen, it felt like I was trying to reinvent the wheel. Are there any good resources out there on standard business processes like payment including chargebacks, payment reminders etc.?

Bonus question: Can you integrate post-paid and pre-paid into one state machine or should you create two state machines and your order object decides which state machine to use?