Thanx @russhwolf, yes I saw that, and looked at that page (but thanks for the reference) and have included that plugin too, but still no dice.
I s'pose the bit that I missed from those instructions was "Re-import the project". I'm guessing that means re-import into XCode*?
The JB KMM docs seem to be very lax about mentioning which platform which actions are on. I'm sure it's obvious if you know what's what, but then if I knew that I wouldn't be looking at the docs 😞