REST is in development mode, and in this mode the System API’s are not yet fully functioning. As of now you can only access the REST API with a Computer (or other device) in the same network as the Gateway.
So to help you move forward, please ignore the System API’s. I’m a Postman fan myself… so here’s a collection you can use to test/develop the REST API.
Please let us know if you find any issues or have any kind of feedback regarding the API. Will appreciate it very much.