The check should be made through the VE-Checker and the connection to the multiplayer server should be checked both directly and through the tunnel.
It is possible that the user is connected through a firewall that blocks the multiplayer network packets. In that case the direct connection would not work but it would work through the tunnel.
SOLUTION:
The user must manage with the system manager of his network so that the firewall allows the traffic through the ports needed by the platform (by default they are 9339 TCP and 9987 UDP).
Contact your company's IT team.
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