Error in SSL Encrypt certificate generation in VestaCP, how to fix it?

Question

Digital certificates

Hello everyone, I decided to set up my server for sites, I did this before, it worked without problems.
Now everything is OK, I installed ubuntu server 16.04 and VestaCP (so as not to bother and quickly set everything up), everything works, but when I try to generate a certificate for a new domain, it gives an error: Error: Let's Encrypt validation status 400. I
searched the Internet for solutions , but I haven't found it yet, maybe someone can tell me what the problem is.

I used to raise the server on VirtualBox, everything worked, now I switched to real hardware and that's the trouble.

Answer 1

After half a month, and an uncountable number of server reinstallations in an attempt to pick up a web panel in which everything will work (since there is still not enough skills and patience to lift everything from the terminal and configure it).
I put the message again, everything works except for mail and certificates, maybe I decided some temporary glitch with LetsEncrypt, I ordered the cheapest paid certificate and there was a problem during validation. The hoster says - we do not see your site on your server from outside ... I check, and indeed - the server from outside is not available. I then tested everything inside the network (both on the internal IP and on the external and connected domains).
I got into the settings of the router (Mikrotik) and it turned out that I was in such a hurry that I forwarded the ports within the network, registered masquerades for ports, and external forwardings were configured on the old IP of the virtual server.
Corrected the IP-shku to a new address and everything works.
Don't be me - take your time and carefully double-check your settings.