not sure what rdm stands for …
You might want to fiddle around with SoapUI if you are new to REST API like I was about two weeks ago.
https://dashboard.hologram.io/api/1 is the service endpoint
/csr/rdm is a resource
With this, if you create a GET method and pass your apikey as a parameter, it will list all CSR messages (messages in the dashboard console).
If you create a POST method and pass a json string with your apikey, deviceid and data , it will send a message to your device and you should see in the dashboard console a response message from your device or a timeout error.
“apikey”:“your key here”,
“data”: “Hello, Hologram!”