Enter a steam API key
In most cases, a steam API key is required or some of your players will not be able to join and your console will output this error: 
This is how to enter a steam API key to solve this issue.
Go to http://steamcommunity.com/dev/apikey
Login with your steam details
Enter a domain name that you like. Could be: "game.vibegames.net"
Copy your KEY
Login on your game panel
In the server overview, click on the name of your server
Click on Startup
8 Enter your Steam API key in the Steam Web Api Key box. Then save it.
restart your FiveM server.
It should work now :)
This is how to enter a steam API key to solve this issue.
Go to http://steamcommunity.com/dev/apikey
Login with your steam details
Enter a domain name that you like. Could be: "game.vibegames.net"
Copy your KEY
Login on your game panel
In the server overview, click on the name of your server
Click on Startup
8 Enter your Steam API key in the Steam Web Api Key box. Then save it.
restart your FiveM server.
It should work now :)
Updated on: 18/10/2020
Thank you!