1.) Don't use httpie for the examples. It isn't standard and it is confusing for those who have no experience with it. I had to navigate to the httpie website to see how the tool works just to look at your documentation because you say that JSON is required but your documentation doesn't use valid JSON because httpie does the work for you. I would suggest using curl for the examples.
2.) I'm curious as to why you are using POST for almost all the requests.
3.) Are you adding more endpoints to this service? I'm curious the motivation behind the current functionality as most of it seems to be very niche in how applicable it is.