ERROR IN SUB DOMAIN CREATION

I wanted to create a sub domain to my paid domain shrinidhi-enterprises.in. I followed the steps below:

1.       In ZOHO SITES, I created a site yogamuni and did preview site. Before publishing

a.       Created a free subdomain www.yogamuni.zohosites.com

b.      In ZOHO MAIL -à DOMAINSà ADD DOMAIN and enteredyogamuni.zohosites.com in Domain screen (given below). A red colour msg ‘YOU HAVE REACHED THE FREE DOMAINLIMIT.UPGRADE YOUR PLAN TO ADD MORE DOMAINS’

 Queries:

 How many sub domains I can have for the paid domain?

Why it says you have reached limit.?

Then how to create a sub domain to my paid domain?