That can have different reasons. We'd like to describe a few scenarios and why a domain registration would not be possible.
The domain name is already taken
In this case, the domain has already been registered by someone else. Unfortunately, a domain can only be registered once (at a time). Therefore, another registration of the same domain name is unfortunately not possible. At least not, until the domain has not expired.
Domains of the desired TLD have special requirements
For some top-level domains, the registry in charge dictates that you need to be a resident of a certain country in order to register a domain with that TLD. In such a case, we may be able to offer you a so-called trustee service so that you can register the desired domain anyway. Whether or not such a trustee service for your desired TLD is offered by us, can be found on the detail page of the respective TLD. Those pages can be reached via the overview of all available top-level domains.
The domain is a premium domain
Some registries have defined so-called premium domains for their TLDs, for which they want to charge more money than for other domains. Unfortunately, these domains can currently not be registered with us.
The TLD of the desired domain is not in our portfolio
Our portfolio includes many different top-level domains. Nevertheless, we may not support your desired TLD at the moment. In that case, please reach out to us and we will check if we can add your desired TLD to our portfolio.