We plan on shipping a billing system for Sampa some time between now and the end of times. I've never done this before and as far as I know there is a lot of little details.
I'm looking to borrow a developer's brain that has done a billing system for their startup recently. Anyone is interested in coffee or lunch (I pay) to tell me about the dirty side of building a billing system?
Sorry for being picky about it, but I'm not interested in business people or program managers. I really want a developer that got his/her hands dirty defining the schema, doing the API, testing it, etc.
Also, Sampa is not e-commerce type of billing (one time transaction). We (will) have a subscription model, so I care about startups that have similar models.