The System API’s are not yet completely activated. As of now you can only consume the REST API within the LAN.
So to help you move forward, please skip the System API calls, you will be able to consume other API without authentication.
We have a collection of API’s to help get started and that’s what I would recommend, you can use the Postman REST Client to start testing, here’s the link of collections:
Please let us know if you find any issues or have any kind of feedback regarding the API. Will appreciate it very much.