Looks good so far. Continue to the next step in the guide.

You must set formRequest = THE_ENTIRE_API_RESPONSE as JSON, not as a string.

This is not a well-formed form_request object.
You can get a form_request using the "Create form request" action of the API or in the API's interactive documentation.

It looks like you copied the docs' example form_request response. Create your own form_request and use that instead.

Start form W-9