MP seems to work fine, but won't on own server

I’ve learned how to customize my server, port forward, add mods, and do all the necessary things someone who’s new to this can do - However I’m stuck now; My server says everything is okay but when I try to join it I can’t. I keep getting different socket errors. Direct Connect works only sometimes and obviously the M/S is 0. Joining other peoples’ servers… No issue there. So it’s on my end for sure and I need help.