autodesk forge – Converting to svf format using Model Derivative API

I want to try my rvt file converted to svf file format using your “Model Derivative API”. I need to keep this in my local. I’m using your api for this, but I’m getting an error like this “diagnostic” : “Invalid ‘design’ parameter.”

Is this error due to the “urn” part? If so, what should I enter in the “urn” parameter and how do I get the svf zip file.

I would be very happy if you tell me what to do about this api. Since I am new to api and Forge api, I would appreciate it if you could help me.