Usage: SERVICES SET REGCHAN <disable|open|opers>

This command will configure how services will allow users to register channels. You can disallow all users, let all users or only allow server operators:

Disable: Channel registration is not enabled.
Open: All users can register channels.
Opers: Only Server Operators can register channels.

/as services set regchan open
/as services set regchan opers
/as services set regchan disable

You could, in theory, only allow the registration of rooms. But since having a registered room requires a registered nickname, this is not a generally useful configuration. You can disallow both, allow both, or allow only registration of nicknames. The advantage of only allowing nick registration is that you can set up all the rooms you want in advance and then close registration.