That your server is not listed in the FiveM server list, can be a result of a few issues. We will tell you here what these issues are and how to solve them.
License key issue
Check if your FiveM license is not used by another server. This will cause your server to glitch on the FiveM server list.
If you bought a key from a reseller then there is a high possibility that he is scamming you and selling the same license to multiple servers.
In your server.cfg there is a variable #sv_master1. Some customers uncomment this variable by accident. DO NOT DO THIS. If you remove the #, your server will not be listed.