FiveM: my server is not in the list or will not let players in

Go in this order: it runs from most to least common.

1. Is it really running?

Check the txAdmin (or FXServer) console. If there are red errors at start-up or the server restarts in a loop, the problem is there, not in the network. Also check it is listening:

# Windows (PowerShell)
Get-NetTCPConnection -LocalPort 30120 -State Listen
Get-NetUDPEndpoint -LocalPort 30120

# Linux
ss -lntup | grep 30120

2. The ports: 30120 on TCP and UDP

The number one mistake. The server list uses TCP and the game uses UDP: with only one, you either do not appear or you connect and get kicked. The commands are in the FiveM ports guide.

3. Try connecting directly

In FiveM, F8 → connect YOUR_IP:30120.

If you get in this way but are not in the list, or you are listed but cannot connect from it: it is the key or private mode (points 4 and 5), or simply that the list takes a few minutes to update.
If you cannot get in this way either: it is the ports, the firewall or the filters (points 2 and 6).

4. The licence key

With an expired, deleted or mis-pasted key, the server starts but does not register in the list. The error shows in the first lines of the console. See the licence key.

5. Not set to private

If your server.cfg has a sv_master1 "" line (or sets sv_master1 ""), your server shows as private: it appears in the list, but with the connect button disabled, and players can only join with connect. Delete it if you want people to join from the list.

Do not confuse it with sv_endpointprivacy true: that only hides your players' IPs in the server's public reports. It is on by default and best left that way.

6. AntiDDoS filters (Spain servers)

In your service's Security tab, apply the one-click FiveM filter. If you made filters by hand, 30120 must be there on TCP and UDP. See the filters.

7. They get in but are kicked while loading

A broken resource: the console says which one fails at start-up or when the player joins.
The database does not connect: oxmysql errors in the console; see a database for FiveM.
A different game build: if you use sv_enforceGameBuild, players need that GTA V build; the client downloads it, but it takes a while.
Very heavy car or map packs: the first download takes forever and some clients give up. Also check you are not short of RAM (how to check).

Still not working? Open a ticket with the IP, exactly what you see when trying to join and the first lines of the console.