Add No-Subscription Proxmox Repository

You’ll need to edit the sources.list file for apt.

Drop this into a .sh script and execute with /bin/bash scriptname.sh

#!/bin/bash
cat > /etc/apt/sources.list.d/pve-no-subscription.list << EOM
# PVE pve-no-subscription repository provided by proxmox.com,
# NOT recommended for production use
deb http://download.proxmox.com/debian/pve $(lsb_release -cs 2>/dev/null) pve-no-subscription
EOM

apt-get update -y

OR

Sources