The reMarkable Paper tablet and the desktop and mobile clients use the same API to transfer files from and to the cloud service. This is an effort to document the API so it can be used to implement custom clients to upload, download and manage files on the reMarkable.
A sample implementation in PHP is available in this repository. Running the PHP command line client with the
--loglevel debug option will print payloads and responses, so you can see how most of the API actually works.
The API is split into multiple endpoints. All requests are made over HTTPS and use Bearer Authentication aka. Token Auth.