backend_plugins
Due to the way our syncing algorithm works, we are no longer able to support the backend API. It is possible that it could return in the future, but it would be a rather large project which we don't think is high priority at this stage.
If you were hoping to create a plugin which makes use of the backend API, we suggest that instead you try to build it via the frontend API.
For example, instead of writing a program which sends data to RemNote from a third party service, use a frontend plugin to request data from the third party service each time RemNote loads and import the data.
For a real life example of this, see the Readwise plugin which used to use the backend API, but has been rebuilt as a frontend plugin.