Quick answer: FiveM connection issues: open port 30120 TCP+UDP, set sv_endpointprivacy false and wait for server fully started (txAdmin green).
If you landed here: "Connection failed", "Failed to connect", timeout or server not in list.
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Frequently asked questions (FAQ)
FiveM connection failed – most common cause?
Port 30120 TCP+UDP not open in firewall/panel. Second: server still starting or license key IP mismatch.
Server in list but join fails?
Set sv_endpointprivacy false, check firewall, enable OneSync. Players: F8 → connect IP:30120 to test.
Only some players can't join?
Often missing client mods/resources, outdated FiveM version or antivirus blocking FiveM.