I have openend a minecraft server for my friends and I, but I have an issue. Anyone with a different IP can connect (tested by connecting via Mobile Data Tethering on my phone), but anyone with the same public IP address as the server cannot connect (tested on different computers/ports with different IPs (such as public IP and the server's IP)) (if it's any use, the error when I try to connect is: io.netty.channel.AbstractChannel$AnnotatedConnectException: Connection refused: no further information). I have tried restarting the router, as well as the server and I have no different outcomes (and yes, I do have my server open).
Note: I did read similar posts to mine, but none of them seemed to be able to help me out.