If you go with the JSON body, set a header Content-Type = application/json , and turn off Private where you want to pass in values on the workflow step.
If you go with the form header, set a body type of Form, the body params will look a little different.
Raw body is useful for edge cases, click the raw tab in Postman body to see the structure.
That Params tab would be for URL parameters, i.e. they are part of the query url.