Make sure you have Qemu Guest Agent enabled in Proxmox!
This is because the port is incorrect in the qemu guest agent config.
Login on the VM and open the file `/etc/conf.d/qemu-guest-agent`.
Now change `GA_PATH` to the following:
/etc/conf.d/qemu-guest-agent
GA_PATH="/dev/vport2p1"
Now restart the guest agent. Also don't forget to add it on startup! To make it run on start simply enter `rc-update add qemu-guest-agent`.