My web server is (include version): Synology DS918+
The operating system my web server runs on is (include version): N/A
My hosting provider, if applicable, is: NameCheap.
I can login to a root shell on my machine (yes or no, or I don’t know): Yes if I enable SSH, but it is not currently enabled.
I’m using a control panel to manage my site (no, or provide the name and version of the control panel): I am using Disk Station Manager 6.2.2-24922 Update 4.
The version of my client is (e.g. output of certbot --version or certbot-auto --version if you’re using Certbot): N/A
My ISP doesn’t support ipv6, so I don’t have a AAAA record with my domain provider, just a CNAME record. I thought that this means Lets Encrypt would use ipv4, but when I try to generate a certificate, I receive the error “failed to connect to Let’s Encrypt. Please make sure the domain name is valid.”
Your vee.house doesn't have an ip address. That may (or may not) be a problem using Synology (I don't know it). Perhaps add the same CNAME to your vee.house domain name.
Ok, so what I’m understanding from what you said is that I need to check if my ISP and router will allow incoming connections over port 80? And then I need to associate an A record IP address with the vee.house domain?