If you receive an invalid token message, then the password verification email has expired. Logout and then back into your Ozobot Classroom account, and select Resend Email next to Check your email to verify your account located at the top of the dashboard. Then verify again through the new email that is sent within ten minutes of the email being received.
Alternately, you can try the Forgot Password option to reset your password. Resetting the password has the same effect as verifying the email.
Be sure to check your spam folder for the email verify and password reset emails. If you do not receive them, you might have created your Ozobot Classroom using the Google sign in option.