I'm just starting to figure out how to add a premium layer to my extension/app, BrainTool. It uses an extension to control the browser but mostly operates as a web-app running in an independent frame, and reading and writing to a plain-text file that the user controls. Its all served statically from github so I have no back end server. I envision needing to support options for a one-time lifetime payment, monthly subscriptions, and a monthly-pay-annually-with-discount.
I had assumed I'd use something like extensionpay by @glench which, given the right Stripe setup, seems able to do what I need (and btw looks nicely done). In looking for a non-extension based solution most seem to assume I set up something like Firebase or run on a CMS like WordPress.
It seems like a common problem. Any recommendations?