Cant connect on forge server

I set up a forge 1.20.1 minecraft server, it runs fine, but when i try to connect one of these error messages appear:
“Internal Exception: Connection Reset”
“Timed out”
“Internal Exception: An existing connection was forcibly closed by the remote host”

I dont really know what to do about it and googled some fixes but they didnt really work.
Help is appreciated very much.