[chsims1]

Thanks for the clarifications.  I was getting compile errors, hence why I was double-checking everything.  Using the specified board manager version is my first 'port of call.'

Ian

So, still using arduino-IDE v 2.3, but  now avr boards manager 1.6.21, I am still getting a compilation error:
 

Code:

Compilation error: call of overloaded 'round(ArduinoJson6172_91::enable_if<true, ArduinoJson6172_91::MemberProxy<ArduinoJson6172_91::MemberProxy<ArduinoJson6172_91::ObjectRef, const char*>, const char*> >::type)' is ambiguous

Does anyone else use v2.3 successfully,  or do I need to find a v1.x IDE from somewhere?

So no one can help me here? I have tried v2.3 & v1.8 on Windows & get exactly the same error. The error seems to be complaining about the actual code, rather than missing libraries and such stuff.