On your smart TV and quest for the YouTube TV app, add it, open the application, and select already a member. Tap on the sign-in button on your TV then
Go to the link youtube.com/activate or tv.youtube.com/start/enter from your device then enter the code that shows up on the Roku channel, click on next, and now sign in with exactly the same Google account you used for purchasing the YouTube TV subscription.
Within a few seconds all set and you’ll be logged in.
On the off chance that the code is not accepted just start it again and try to complete it as quickly as possible because if you take a more time then the code gets expired.