you have a digital ocean droplet on which you installed virtualmin
Make sure at your domain registrar, you have added custom name server records that enable your domain registrar server to tell the world to ask digital ocean’s nameservers (ns1 and ns2) in order to find the server location (ipaddress) where your website is being hosted
in your digital ocean interface ns records, you need to also add the ipaddress of your droplet and any cname records etc. Otherwise, when the registrar server tell’s the world to go to digital oceans name servers for the ipaddress, digital ocean’s name servers dont actually have any ip address in them yet in order to tell the world what you website ipaddress is. the result will be an error.
Also ensure that you have added a rule opening port 10000 on your digital ocean droplet as it most likely isnt open by default.
as a final check, ensure that you are installing the website for domain2.com into the correct directory in apache. I think from memory apache can use 1 of at least 3 locations for the web directory. Having said this, if you are using a standard virtualmin install from the installer script, im pretty sure it should already be configured correctly anyway (but worth checking just the same)
Goto https://mxtoolbox.com/SuperTool.aspx and use this interface to check if your server and hence website are reachable. I use mxtoolbox all the time, its a valuable tool.
based on your original post above, it appears you are not using Bind dns in virtualmin, so you do not need to manually add any nameserver records inside virtualmin itself. You would do this is only if you have setup your droplet to be one of the nameservers (of course you could do this if you wanted to)
EDIT…
a simple workaround for all of the above is to not use nameserver records at all but instead, do the following at your registrar…
go to registrar domain zone records and simply add an “A record” pointing the domain directly at the ip address of your digital ocean droplet where your virtualmin install is located. You may do this for all virtual server on your virtualmin install.
Just 2 caveats about A records at the registrar…
some registrars do not provide free dns hosting
if you have many clients in my opinion this would not be a good idea because if for some reason you need to move servers to a new ip address, then every client website will go offline until they manually update their A records. By having clients instead point their domains at your own nameservers you can control all of this updating yourself without worrying clients to do it themselves.