Each device has a Swagger Interface which can be reached under the URL
http(s)://<DeviceIP>/openapi/swagger-ui
This Swagger Interface allows to use/test the REST-API functionality. At the beginning you need to create a session and Authorize with the SessionID. Next you can upload a PDF or XML document to the device. The user can see this document and start the signing process. By reading the event queue you get the feedback what the signer did. When the signing process is finished you can download the signed document.