This is kinda a broad topic, but I'm kinda uncomfortable about the fact I still don't really understand how all this payments stuff works. Can somebody enlighten me, what does it take, exactly, to build a payment processor? Can anybody do that, theoretically? Do you have to implement some payments API for every bank your customers will use? In every country? I assume, the API's are not entirely open and are more than just a number of SWIFT conventions, so why would the banks work with you, how would you convince them? What really is a payment system, anyway, what's the difference between using a card and making a bank transfer? Why are there so few credit card providers, how are they different from, well, your future payment system?<p>There are many questions beyond that, but it should be enough to judge the level of my ignorance. So, maybe somebody knows a book, a set of good blogposts, a really long YouTube video? Something?