Host name cannot be changed in Net4 DNS settings

My subdomain is hosted on Net4 and I want to transfer my pro app onto the subdomain for which I have to add Cname and Txt records.
I could add the Cname record but while adding the TXT record, I am unable to change the host name to because it says the host name cannot be other than the domain. Is there something I am doing wrong?

Hi Mehta, where you actually able to solve the issue? I am asking because my german hoster does not allow either. They only allow for so without the _underscore !!!

No I didn’t take more effort, changed the domain host