i'm sure they are running the same configs and mods as i took the mods folder and config folder from the client and gave it to the server
edit: sorry for the late reply only just got off work
edit 2: just recopied everything over again thinking maybe a file broke somewhere and it seems to be working now.
Forge 14.23.0.2522
the game throws the error in the title to any players whom try and join the server. fresh server and fresh world
will comment forge latest logs below (forum doesn't like me posting them both at the same time)
edit: had to link to my google drive for the logs. forum wont let me post them
fml-client-latest.log https://drive.google.com/open?id=15bZo5yymKCCxdKb1MiAwRgh5pV9hqpYl
fml-server-latest.log https://drive.google.com/open?id=1UOoCC0-KKfgN-qj1DxtSvj44eyUfg9XW