Custom URL

Hello

I am trying to access the mail login page through the "webmail" subdomain. I have already configured the CNAME record in the DNS manager, pointing to business.zoho.com. However the url with the subdomain is not working. I suspect it is because the subdomain is not declared at zoho's interface.
I have been reading the forum and it seems one should add the subdomain in the Domains section of the CPanel. However, there is no such option, I pressume because of having a free account.
Are you to add the subdomain manually? Or is it not possible for free accounts to have such a subdomain?

Kind regards