I've been looking into how to structure a subscription-based payments platform for a plugin that I'm building (in C#, in case this is useful), but all information nowadays is centered around SaaS.

There have been discussions in HN about on premises B2B software and their differences (and advantages) over subscriptions; but nothing about how to manage yearly billing, subscription management, etc. a la chargebee.com, and I can't seem to find material that is not focused on building the whole thing yourself from scratch.

Does anyone here have an application / plugin / etc. that is locally installed in the client machine, and for which a license needs to be purchased and installed? If so, have you programmed everything from scratch, or are you using some specific commercial service to outsource all that complexity?