The domain in the screenshot does not resolve. So, are DNS records from this domain set to the IP adres of your VPS server ?
I would suggest using the NS from your domain registrar, Namecheap I believe? After that, set the DNS records to your server IP. Note: NS change may take 24h, DNS is often a bit faster, so be patient :-)
If the domain does not resolve, you can't isseu ssl
Hope this helps