DENIC, the registrar for all .de DOMAINs only accepts name servers that meet certain criteria.
Documentation: Nameserver Predelegation Check
The test must be passed successfully, otherwise the name servers are not entered. A .de DOMAIN without a valid name server will be deleted by DENIC within 30 days!
With the NAST web interface you can perform a name server predelegation check. The name servers of your zone (DOMAIN) are subjected to various tests to ensure that they are correctly configured and that the DOMAIN can be delegated safely and easily. This guarantees a high quality DOMAIN.
Please test the desired name servers in the web interface provided by DENIC. Please enter your domain name in the form. This is, of course, only possible with already registered domains.