Cannot find Plan option when creating subscription for a customer

[iltera]

The title says it. When I create a subscription which is not under any clients, there is a "Service Plan" option. But it is not there when I create the subscription under a client. Is there a specific reason for that or its just missed?

EDIT: Never mind, I needed to choose "Subscription" tab from the tab when adding a subscription. The default is domain and I was adding a new domain.