Not able to create sub-domains
I purchase
jobtrackable.com from Zoho and I have been trying to create a sub domain
app.jobtrackable.com but it is showing an error. I only want to create a sub domain and don't require any email associated with that sub domain. I am on the free plan but I fail to see why I am not allowed to create a sub domain. All domain providers have this feature but only Zoho seems to lack.