domain name is not pointing to the same Name Server for the main domain

Referring to the reported issue, we have checked on your issue, you are getting this error due to the domain name is not pointing to the same Name Server for the main domain.

However, there is an option on WHM you can enable it. >Tweak Settings > search > Allow Remote Domain> turn it ON > Save. this will allow you to add the domain with out setting the DNS.