Thanks for reaching out to the Chromecast Cast Community! Let's sort this out.
A few questions: are you using the Google Home app to set up your Chromecast with Google TV (HD)? If yes, what mobile phone are you using? Have you tried setting it up via the Chromecast Voice Remote? What exact message are you getting when signing in to your account?
Give these steps a try:
Let me know how it goes.
It looks like you've posted your concern twice and I've responded to your other thread.
I'll merge this to your other thread. Let's continue the conversation there as this will be locked automatically once merged successfully.