The parameters you provided for the request body look valid.
We assume the content type of the request might be incorrect,
because HTTP error 415 indicates “Unsupported Media Type”
I prepared a small example for you, using our demo instance.
The example sets the content-type to application/json.
Regarding the error codes I will look into improving the documentation.
For testing purposes I can recommend to give the Curl utility a try.
It allows to send HTTP requests from the commandline.
The NetHSM API documentation can provide you the respective command when you click the “Try it out” button under an endpoint.
Please don’t hesitate to reach out if you have further problems or questions!