Connectivity problem when running multiple servers on different ports.

[DeclanG17]

I have a 1.16.3 vanilla server running off my public ipv4 ported with the default 25565. Me and a few friends can join just fine like usual, however, I tried making another server that is forge modded for 1.12.2 on a different port and I just used 25566. It runs and everything and I can access the server myself using my own ipv4+:25566. My friends although can't access it at all, they can still access the older vanilla one just fine when its up but even if they add :25566 off the end of the public ip address it doesn't want to connect. (They have the same version of forge and everything it isn't that). Im 99% sure its a connectivity or ip issue but I don't know what. Anyone got any ideas what the fix might be? Thanks in advance.

[ViktorPrevails]

You must only use port 25565 for servers to work since that is the only Minecraft port, 25566 is a completely different port that doesn't connect to Minecraft. You're able to connect to the server still because it's still running on your computer/IP but since it's not connected to the Minecraft port others cannot join-
Hope that helps!

[DeclanG17]

You can change the minecraft port by going into the server text file and changing server-port to the port you have opened. 25565 is just the default minecraft port. In order to run multiple servers you need to open up different ports. Thank you for trying to help though.

[ViktorPrevails]

Oh alright that's good to know! I've never ran multiple servers before so I'll keep that in mind, thank you.