[jingai]

There are no cards, but Alexa has picked the command up because I can see it in history. The blue rings just disappear. I've tried play movie (plays random movie in test app), pause (again works fine in test app).

You are remembering to invoke the skill, right? "Alexa, play movie" won't work, for instance, but "Alexa, ask Kodi to play movie" should.

Try a command that doesn't involve the words play, pause, stop, skip, etc. Like, "Alexa, ask Kodi to watch a random movie".

Also, please look at your server logs (Heroku, Lambda, etc) to see if the request is making it there, and if so, what it's saying about it.

It isn't anything to do with me being in the UK with a UK echo, and lambda is hosted on us servers?

No idea, honestly.