Error/moodle/confirmationnotenabled

1. Login to Moodle as an admin
2. Go to the Site Administration tab (<domain>/admin/search.php)
3. Search for "registerauth"
4. Set it to some value other than Disable

It is also possible that this error may arise if you have somehow selected other auth plugin and that plugin does not implement the can_confirm() as returning true in its auth.php config file