/api/v1/. It accepts JSON request bodies, returns JSON, and uses standard HTTP status codes and bearer authentication.
It does three things, all for your per-user door:
The public door needs no API: the site token in your page is enough. See Quickstart.
Client library
@concatflow/node is the official library, for Node 18 and later. On any other stack, call the routes directly: the examples on each route page are in cURL, Python, JavaScript, Go, Ruby and PHP.