The ability to set NS records in our DNS control panel is intended for “re-delegation” to another set of nameservers (not Tibus). This redelegation is only possible for sub-domains (e.g. mysubdomain.example.com):
mysubdomain.example.com NS something.ns.cloudflare.com
mysubdomain.example.com NS somethingelse.ns.cloudflare.com
You cannot re-delegate the root of your domain (e.g. example.com). Changing the NS records for this domain root is possible in the DNS control panel but it will not have the intended effect.
If you need to delegate the domain entirely, please contact Tibus Support. who will make the change at the Registrar for you.