do you know

https://forum.processing.org/topic/simple-json-example-with-api

Thanks for this.. 

I downloaded this library: https://github.com/douglascrockford/JSON-java/downloads, into my sketch folder / library folder.  Is that the correct org.json library?  If not, where may I find an up to date library? 
(This library, after being installed, just leads to the same error):

No library found for org.json
As of release 1.0, libraries must be installed in a folder named 'libraries' inside the 'sketchbook' folder.

Wiki: How to Install a Contributed Library

maybe use the one by a__g

https://forum.processing.org/topic/json-library

your api supports xml as well, i would go for that since i think it's more easy.