How to access/reference JSON payload accepted at endpoint later in the function stack?

Hello, I've created an endpoint to accept a POST from TypeForm, which has a JSON payload.

How do I reference the payload received in the request to the endpoint?

I can see the payload when I click 'Request History' in the menu for the endpoint, and can traverse the JSON there. But, when I try to reference it in the function stack, I can't figure that out.

I would expect that the JSON object received would be able to be referenced using some type of dot notation.

For example, given the request below (screenshot), if I want to get the 'invite' value, I would expect something like:

requestbody.form_response.hidden.invite

However, there doesn't seem to be an object called 'requestbody' or anything like that.

Is there a way to 'pre-define' the structure of the JSON that I am expecting at this endpoint such that I can reference it in the function stack?

I tried to make the endpoint's input type 'JSON' but then somehow what's received isn't correlated with the actual payload.

Thanks in advance for pointing me in the right direction here.