Hi,
Could you please confirm which wizard you've opened to register the domain name?
It will be more appreciated if you could share us the step by step guidance you've followed to configure the SBS server?
Kindly check below blog and try to find out the relevant logs of this Domain name registering failure issue.
Key Small Business Server 2011 Essentials Log Files
https://techcommunity.microsoft.com/t5/windows-server-essentials-and/key-small-business-server-2011-essentials-log-files/ba-p/398341#:~:text=In%20SBS%20Essentials%20the%20location,log%20file%20will%20be%20located.
Thanks,
Jenny