Friends get an io.netty.channel exception when connecting to my server

I just set up my server the other day, I’m trying to make an ATM6 server for a few of my friends to play on. I’ve used MineOS a tiny bit in the past and decided to turn my old gaming pc into a server because I needed the RAM to host the modpack server.

ANYWAYS, I’ve set everything up and it runs, but I am the only one who can connect. I’ve run minecraft servers in the past without MineOS, so I know a little bit about port forwarding. I thought I did it all properly for port 25565, but the only solutions I’ve seen for this issue are port forwarding solutions. I’ve also messed with the iptables a bit from what I found, but I’m not sure if that’s the problem. I’ve seen a few things about firewall issues and such.

I just need a point in the right direction. I can connect, but my friends can’t. :frowning:

Edit: Something I forgot to add that I’m not sure has to do with anything. I currently have two routers, one main one and another being used as an extender. Not sure if that could be part of the problem, but I thought I would add it!

Edit again (sorry): I’ve figured out how to double port forward, but I’m still having the same issue.