Yes...I spotted that...
This is exactly why CPAN Testers is so invaluable...I have JSON installed and had wrongly assumed it was core.

So I have to make a call whether to use JSON or JSON::PP
At first I thought JSON because it will default to JSON::XS if available. But then I reasoned that JSON::PP would be better because it is core and, in this module, it will only ever handle modest JSON objects after an HTTP call so speed is not a massive factor. So better to go for a core module at the possible expense of a little speed.

Is that logic sensible for this choice?