Plesk 12.x / Linux :: Web Admin Edition - Cannot Create Extra Domain

The license says that it provides 10 domains on the License Management page. However, when I try to add a new domain, I get:

Code:
Warning: Permission denied.

When trying to add a domain from the command line, I get a warning that I can't add a new subscription (which is probably the way Web Admin works, 1 Subscription, 10 domains):

Code:
# plesk bin domain --create test.be

An error occurred during domain creation: You cannot manage subscriptions due to license restrictions.

How can I use all 10 domains?