Hyper uses the Credential Manager to store your YouTube account.
There must have been an issue while signing in and something went
You can try the following:
Remove your account by going to the Credential Manager in
Windows (just search "Credential Manager" from the Start Menu). In
the Credential Manager under Web Credentials you will see an entry
for "HyperForYouTube" - click this credential and click remove at
Now when you restart Hyper, it should allow you log in again. If you linked your account to a YouTube channel, it should now work.