>how would you have any guarantee that your third party solution would be able to support those... You could say the same thing about literally any 3rd party s

>how would you have any guarantee that your third party solution would be able to support those... You could say the same thing about literally any 3rd party software or service you purchase. "Why use cloud services to do anything?" etc. Sure this thinking will hold for some things, but chances are that for something as standard as billing you're not going to be implementing some revolutionary feature that gets you more customers. On the other hand, if you mess up billing because you rolled your own system that doesn't have many standard options that a mature OTS system would offer it can lose you potential customers, because for months at a time you're stuck building the most mundane and standard things like an annual plan that could be used to better appeal to buyers. Survey the main OTS options and see what they can do. It will probably give some ideas like "Oh yeah annual plans, we'll probably want them at some point". At the very least you do this at the outset when you're small. Worry about complex billing requirements that won't be part of vanilla options in most OTS systems once you're big enough & complex enough to require them. Otherwise you're worrying about a Maserati problem.