[sanjonny]

Adding API keys is not working for me. All I get is "LOGINEXCEPTION:[401] UNATHORIZED_CLIENT". These are new keys (I didn't have a use for them before). I've turned off "use developer keys". I've used copy and paste to make triple sure that I copied the correct credentials in for API key, AIP ID and API Secret. I've tried uninstalling (though Kodi doesn't allow me to uninstall the YouTube addon due to a dependency). I've tried clearing and deleting all the settings etc and running the setup wizard.

It's just not working for me.

Here's to hoping an update can fix this problem for all of us.

Did you do "remove user" after you added the API key? I had to reregister the app from scratch after the keys were inserted. And then it worked. You could also try deleting the addon from your OS instead of inside Kodi. Since you can't remove it. But for me, I didn't have to remove anything. Just remove the "default" user in the addon settings and then do the two auth requests again on google.com/device or what ever. The name of the API access should then show up during registration.     

I would also add I ran into numerous problems getting it to work even though I had a valid oauth setup in the past. Three things I found. If you have not used your api id in awhile, it is deleted deactivated by google (found this on an authentication forum)

*****EDIT, Just start a new api.
 If you hand create the api key or the oauth key without doing it thru the enabling the youtube v3 and using the create credentials dialog, it will fail, (also from another forum) neiither of these are documented. So process should be
If you already have an old api id, just delete it, rekeying will not work if it has been more than 60 or 90 days
Follow the github guide https://github.com/jdf76/plugin.video.yo...l-API-Keys, but basically
1 create the developer account
2. enable the youtube v3 api...YOU MUST USE THAT dialog to create the oauth credentials FIRST (on my screen, the create button was on the right after enabling the api), and the consent screen, give a name then CREATE the api key. Doing it in a different order or creating the oauth without doing it when you first enable the api will fail with the eventual error message of you have not enabled the api when you try in kodi....
3. First check the setting in app is set to personal and make sure allow developer keys is off. I found it easiest to copy the keys and secret via the web interface in the app Enable the api configuration page, to enable this go to the 
Settings - API
 and enable 
Enable API configuration page


You should then be able to update your keys by visiting 
http://<IP of Kodi device>:<port>/api
The port used is 
Settings - HTTP Server - Port
 which by default is 50152
XXXXXXXHUGE IMPORTANT WARNING......You must....
4. Go to maintenance setting and clear the access_manager.json file before you restart if you don't, it will not work. you can also delete that file by hand but heck, you are already in the user interface, its like 4 clicks.
If you don't delete it, it rewrites
XXXXXXEND HUGE IMPORTANT WARNING!
5. Restart kodi. Then do the login scripts. 
There is one part I am unsure of...somewhere in the oath setup about, you pick devices and access. EDIT not necessary ---I had to click to add zone access (otherwise its just email and profile). I do not know if that is required to run the app, but I enabled all the locked youtube. That means they will review it at some point, but you might not need to do that to get it to work. ENDedit. Just leave them at default, I think email and profile...

when you reboot kodi, you should get the 2 google auth screens when you try to sign in.

One final hint, if you are doing it on multiple devices, after the first is set, use file manager to copy apikeys.json (or whatever it is called) to a network location so you can just add that to the next kodi box. I believe the file is in profiles/add_ondata/plugin.youtube.whatever. That saved time doing my 4 boxes as you just copy that file to the new device using filemanager, then start at step 4 above, saves you all the cut and pastes, restart and do logins.
If I think of anything else I will add it, but once I figured it out, got all 4 boxes up in about 7 or 8 minutes. On my devices where I just copied the files, I did not change user status at all, becuase wiping accessmanager I think does that anyway. I will try it out more later but hopefully that solves your problems.