Assigning a valid SSL cert to HTTPS secure a VPN host

The Problem So you want to assign a valid SSL certificate to a host on a VPN, on which you have a subdomain under a domain that you have zonefile access to, where the subdomain points to your host’s VPN IP, and the host requires a working HTTPS server. The issue comes into play when you try to use certbot/letsencrypt/[insert ACME client here] to generate the fullchain and private key, beca...