How to use the SaveSourceScreenshot call?

[CaptSzat]

I am trying to use the SaveSourceScreenshot but it keeps giving me a 702 error.

Could anyone point me in the right direction? I know I am connecting to the websocket fine and I ahve been able to get other calls to work but I seem to be doing something wrong here. Here is the documentation https://github.com/obsproject/obs-websocket/blob/master/docs/generated/protocol.md#savesourcescreenshot . This is JS.

Heres my code,

let dataRequest = {
  sourceName: "Testing",
  imageFormat: 'png', 
  imageFilePath: "C:\test\screenshot.png"
}
....
await obs.call("SaveSourceScreenshot", dataRequest)