How to open port on HAOS for ADEMCO/SIA alarm events?

Hi, I have a Proxmox with HA OS VM.

I’ve installed an integration (not addon) that can listen SIA DC-09 protocol (SIA Alarm Systems - Home Assistant), i’ve configured it to listen on port 751. the integration say to choose a port not used by any other process in HA so i decided for that randomly.
No message is received. i suppose because the packet could not reach the integration on HA VM.
i have no firewall.

any help?