[SlimTrigger]

Ok I think I got it working... someone else who has their's working should confirm that I've got this documented correctly...
(if this doesn't fix, or you mess things up you should be able to uninstall and reinstall the youtube plugin and it will reset to the default settings)


First uninstal the YOUTUBE addon (you probably don't have to do this but it was just cleaner this way I didn't have to delete any folders)

Then reinstal the YOUTUBE addon... don't sign in

Close KODI


Thent go to
https://console.developers.google.com/apis/

Click on Credentials, then New Credentials, then API key, and select Browser Key, give it a name and click Create (this creates the KEY)

Then back to Credentials
Click on Credentials, then New Credentials, then OAuth Client ID, select Other, give it a name and click Create (this creates the ID and SECRET)

At this point you've got 2 sets of credentials

Locate the file - login_client.py
(On Windows it's located here - C:\Users\username\AppData\Roaming\Kodi\addons\plugin.video.youtube\resources\lib\youtube\client

Within the file login_client.py find the section that corresponds to the version of KODI that you're using in my case I'm running version 15.2

youtube-for-kodi-15': {
'system': 'Isengard',
'key': 'aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa',
'id': 'bbbbbbbbbbbbbbbbbbbbbbbbbbbbb.apps.googleusercontent.com',
'secret': 'ccccccccccccccccccccccccccc'

Set the Key to the Browser API key you created first
Set the ID to the OAuth Client ID you created second
Set the Secret to the Client Secret shown in OAuth Client ID

(Make sure that you're copying and pasting these between the quote marks)

Save the updated login_client.py file

Then launch KODI
Select the YOUTUBE Addon
Select SIGN IN

Then do the 2 x activation thing where you go to
youtube.com/activate

Enter the code from KODI, click NEXT then click ALLOW
Then enter the second code from KODI, click NEXT, then ALLOW

And that should be it... mine seems to be working...

Which Developer API's do you have active? I have the YouTube v3 API active but, just having that one seems not to allow me to access my WatchLater, History, or Liked Videos playlists (oddly enough the Disliked Videos playlist shows just fine). Before I activated the YouTube v3 API, I didn't get anything from my actual account so I know that was part of the problem.

Folks, I'm a newbie to this, and for others in my same boat, let me emphasize that the Activoice instructions absolutely will work BUT IT IS IMPERATIVE you pick up on what CardCaptor is saying - that is, you HAVE to enable the YouTube Data API when you are in the Google Developers Console.

If you refer back to the Activoice instructions - AFTER you get the two sets of credentials, while still in Google Developers Console, make sure you are in the API Manager, on the Overview tab. Click on Enabled APIs, and if you're new to this, the list of Enabled APIs will NOT include the YouTube Data API. So, click on Google APIs and under the YouTube heading you will find the YouTube Data API. Enable this API.

Then, it's back to the Activoice instructions!

Hope this is helpful for some of the other rookies...