[ifelsethenend]

That's correct - you need to put in two different codes, one after the other. After the first activation page says 'it's done go back to your device' the input code on your Kodi display should change. You then have to open "youtube.com/activate" (or google.com/device, that seems to be the current URL?) a second time and put in the second activation code -> this is the activation of your personal API keys, as far as I recall.
Hope that helps!

Regarding your problem with video playback I think you will need to post a debug log so the problem can be identified. There's a short how-to on the wiki. 

Just tries it again now, but the code on the screen doesn't change at all. I tried reloading the activation page again and inputting the code too.
I used Kodi Logfile Uploader and here is the link: https://paste.kodi.tv/aducuqibuy

Thank you for your prompt reply.