You must first obtain an api key:
Click in the Phoscon app => Gateway => Advanced => Authenticate app.
And next use the following REST Api command:
POST http://192.168.25.25:40850/api
With in the body:
{ "devicetype": "my application" }
As a result you get your restapi-key. So your command will be:
GET http://192.168.24.24:40850/api/restapi-key/sensors
With this you can get all your sensors from within deCONZ. This will include the Cube sensor(s).
You can read more about this at: https://dresden-elektronik.github.io/deconz-rest-doc/getting_started/