What is wix's JSON structure, when using automations.

I have a web app that handles POST requests, with simple JSON formatting.

I have set up an automation using Wix Automations, that sends a webhook with a customised payload. However, I can’t find any documentation of the structure of that payload. Does it follow a simple JSON structure such as 'payload.postData.contents. ? with JSON pairs? Or is it something else?

Furthermore, is there a way to send a test webhook for debugging?