all NS on 1 ip?

is posible to be all two NS on the same ip? i mean i have just 1 ip and after i instaled this panel, i set ns1.mydomain.com and ns2.mydomain.com with the same shared ip. and to testit if it work, i created a new domain at dot.tk and i used my NS adress on that .tk domain. and works 1-2 days, after that .tk domain is dead. i mean not work.

pls help me.

Yes, you can have both NS on the same IP. Though its not recommended and defeats the purpose of having a secondary name server for availability perspective.

Have you registered your name servers with your domain registrar ? The name servers needs to submitted the registry.

https://www.namecheap.com/support/knowledgebase/article.aspx/768/10/how-do-i-register-private-nameservers-for-my-domain