Usage: SERVICES SET REGNICK <disable|open|verified|opers>

This command will configure how services will allow users to register nicknames. You can disallow all users, require email verification, let all users without verification or only allow server operators:

Disable: Channel registration is not enabled.
Open: All users can register channels.
Opers: Only Server Operators can register channels.
Verified: Used when you want to have email verification for nicknames.

/as services set regnick disable
/as services set regnick open
/as services set regnick verified
/as services set regnick opers

If verified is set then you must have an SMTP server configured otherwise this will default to open.