Unable to add external zoho account using mail.zoho.com or the zoho Windows desktop app

Unable to add external zoho account using mail.zoho.com or the zoho Windows desktop app

Trying to add a second zoho mailbox that exists within my zoho domain.

Using Windows desktop zoho app: Settings|Mail Accounts|+ 

After entering the required info, the Save button is greyed.

I was able to add the other mailbox as a Send As account. So, I can send on behalf of the other email address but cannot view incoming messages sent to the other address.

How can I view email sent to the other address?