UDP send/receive work with editor and not when standalone

Hi All,
I just reused one of the several UDPReceive.cs found on github.
I have an external app made in unity and built that send the message, and the receiver in another app made with Unity as well. If the receiver runs under Unity Editor the communication works and when I build and put as standalone no. I put a rule in the firewall, so it should not be stopped.

Did anybody face an issue like this?
Thanks,
Daniele