Domain name configuration for Lets Encrypt Certificate generation

Hello colleagues,
I am in process of FreePBX configuration and stuck on the stage of Lets Encrypt Certificate generation. In order to generate the certificate, I need to create FQDN. My FreePBX is installed in VirtualBox which has private address and bridging connection. Has somebody step by step instructions how to create FQDN in such configuration and what I need to ask my internet provider to do for me?
Thanks in advance!

I don’t know whether your ISP offers domain registration; most don’t. But whether from them or another domain registrar, you must first purchase a domain name, unless you already have one that you would like to use. For example, you could purchase zeevtur.com at domains.google.com for $12 per year.

Next, you need to set a way for Let’s encrypt to verify that the domain is yours. The most common method is to set up DNS for the domain to point to your public IP address. Most domain registrars, including Google, offer free DNS for domains registered with them.

Next, set up your router/firewall to forward TCP port 80 to the private address of your PBX and FreePBX should then be able to generate the certificate.

If you are on a tight budget and are willing to accept a sub-domain, e.g. zeevtur.hopto.org, you can probably do this at no cost.

Thanks a lot!)