In the HTTPCaller we can specify some settings that will be represented as a Header of the request. For example the Content-Type parameter specified in the Body section sets the Content-Type header of the call. This is not very obvious to see as you can still specify a Content-Type Header in the Header section. Often, if two different Content-Type Headers are set the request may fail, because they compete. The Authentication option also sets Headers behind the scenes.
The Query Parameters show a similar behavior. If we set a Query Parameter it will be added to the end of the request URL behind the scenes. But if this parameter is already part of the URL both will compete.
It would be nice if the Headers and the Query String would be updated on the fly when the URL or a parameter (Body, Authentication) is modified/added and vice versa. The Postman REST API Client is a nice example for this functionality.