Follow these steps if you're facing authentication issues with your zoho account
Login to your Zoho account
Click on this link https://mail.zoho.com/UnblockMe
Additionally go to your admin portal - https://mailadmin.zoho.com.au/cpanel/home.do
Go to your Users list - https://mailadmin.zoho.com.au/cpanel/home.do#users/list
Scroll to the blocked account, you’ll see a Red outline of a person under the Status section, click on them and unblock