I'm going to keep this short, I was using the server which was working perfectly fine for about a week and my PC got the blue screen (like the 4th time this has happened) due to an audio driver issue (not the problem) and the server was forced shut down. After restarting my PC, I started the server again. I was expecting to jump back into making my farm but for some reason, I was not able to connect. I thought it may be a bug and tried to restart it. Still did not work. I tried everything like checking the firewall, resetting my router, checking my port-forward blah blah blah
All that I found was that when I started the server an error popped up in the console:
It really seems like you know your stuff! Could you help me out? My server was working perfectly fine like 16 hours ago but then after a while my friends weren't able to join. I have checked all the stuff like firewall, port-forward and I even re-installed Minecraft. Nothing seems to work. Oh yeah and another thing that is happening is that for some reason I am not able to join my own server by putting Server IP as 0 but I am able to join if I put localhost:25565.
What's up with that? I'm not technical at all so please keep that in mind.
Not being able to connect with your public IP address from inside your network is perfectly normal and not an issue. You should always connect with localhost. Use canyouseeme.org to test your portforwarding.
Turns out the Firewall was indeed the problem! I thought it was fine but my Anti-Virus was taking over and not allowing the server to be public. If anyone else is having this problem, please try disabling your anti-virus for a little while, if the problem disappears, then try and narrow it down from the anti-virus. I'm not very good with English so if what I'm trying to say is not clear, then please let me know and I'll reply back explaining it as soon as I can.
Also, a special thanks to Tails1 for offering to help!