Thanks for the suggestion.
I tried it but I cannot connect to the server.
I make this test:
from another computer in the terminal I do:
nc -zu ip_server vpn_port
For the standrd port 1194 i get:
Connection to ip_server port vpn_port [udp/openvpn] successed!
for the custom port I get:
Connection to ip_server port vpn_port [udp/*] successed!
I tried also from the local netowrk but is the same: vpn with port 1194 works, vpn with custom port no.
Thanks for help!