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It tells you the possible solution to this at the end of the error message: If you just registered a domain and also setup the vps in virtualmin this can happen, since it takes it time to connect a new domain to the internet. Depending on your registrar, your nameservers and your tld it can take up several hours, in some cases even 24 hrs.
Make sure, you entered the correct IP address for your domain and the domainname both in the DNS and your VPS are correct. If that is ok, then just wait a while and retry later.
Best