If you receive this message: Availability check is not available. when registering a domain, it does not necessarily mean that you cannot register the domain. In this case, it is simply not possible for us to check the availability of the domain at the registry, via WHOIS services or via DNS.
To register the desired domain anyway, you can click on the arrow next to the Search domains button and then select: Add domain(s) directly to the shopping cart without availability check.
You can then register the desired domain as usual, if it is not already registered. Of course, you can also inform us about the non-functioning availability check so that we can restore it. To do so, simply send us an email to support@inwx.com.