Json feeder: how to use API response variables inside it ?


I am saving all my requests bodies in json files and i access it using json feeder.
In one of my API, body should have the value, say 'token'. I get token in the response of another API which is executed first. I saved this token from response using "check(header("tokenName").saveAs("token")".I mentioned the token in my json file like ${token}, but no luck. It gives me an error message " attribute name token is not defined".

Any help on this would be much appreciated.It is very urgent for me. Thanks in advance.