If you want change IP nameserver on a .IT domain, or use subordinate nameserver you need to use format nameserver:ip
For example, if you want use nameservers ns1.customer.seflow.it and ns2.customer.seflow.it on domain seflow.it, you will see error:
"ns to add is subordinate but has no ip addresses"
To avoid that please use format
Remember to replace ''hostname and ip with your nameservers host and ips.