I'll look into getting that page updated.

One known issue is that CC doesn't have a concept of a default shared
domain when pushing apps.
The CLI assumes it's the first shared domain that comes back in the list.
Depending how you're splitting your domain, you may need to create a new
shared domain, delete any other shared domains until your desired shared
domain for apps is first in the `cf domains` list and create/map routes
with your new shared app domain to existing apps.

-Dieu