So I got a "Connection request to xxx.xxx.x.xx:25565 failed"

I recently started to make a multiplayer game with an asset, and I got this error, "Connection request to xxx.xxx.x.xx:25565 failed" I don't know what to do.

The asset I bought was MultiLan, and I followed the basic instructions from the documentation. The unity editor did not give me any errors, so the game could run. However, I still receive the aforementioned error in the console. I think it has to do with the port number (the 25565 part) but I don't know for sure.

I saw another post...

So I got a "Connection request to xxx.xxx.x.xx:25565 failed"