Proxmox

Important for network debugging

run this

systemctl restart networking

then tests like

ping 1.1.1.1

For different domain providers (my case is porkbun, don't forget to enable API access on domain manager), look here: https://github.com/acmesh-official/acme.sh/wiki/dnsapi2 (also check web GUI's: ACME>Challenge Plugins> Add>DNS API drop down menu for your DNS)
Securing Proxmox (Source)
Securing Proxmox.pdf

Note: I had the "This site can't be reached"