I'm trying to create my server but I'm getting the red error message:

One of the following suggestions may help you:
Your server is currently offline.
GameTracker needs your server to be online before you can add it to our database. Please restart your server and make sure it's up before hitting ADD SERVER again.
You entered the wrong query port.
Please update your query port and hit scan again
Your server is firewalled.
Please turn off any firewall you have that may block scanning or whitelist the gametracker scanning IP addresses:
149.28.43.230
45.77.96.90
108.61.78.150
108.61.78.149

I've tried it even with my firewall off, and I'm getting the same error so it's not the firewall. I don't know how to check if my server is online, or if the query port is wrong (I'm getting the automatic one). Any advice please?

See: My server will not add or shows as down, what should I do?

You must be certain about your public IP address, port and if the server is online.

There are plenty of advice pages on server creation that can be found via google or other search engines.