if you had that server at another gameserverprovider than ZAP-Hosting (us) it may became blacklisted. You can send the last invoice of your provider to fivem@zap-hosting.com - we will then refund the amount to ur ZAP credit.

If you setup your server on a VPS/dedicated server, you can paste the console output here. Furthermore: Are you able to connect via “direct connect”?