I have an SMP with my friends and I think I did everything right (downloaded it installed it on the server and in my mods folder)
but it just wont work. It works if I load up a single player and use the mod in that world just not in the server.

same problem to be solved

Both client and server needs to install this mod

not this problem, the server cant even launch normally, it would stuck at world loading when this mod is added

@EnderTheCoder post the server log. Does the stuck happen randomly?

And if you are using bukkit4fabric, IP is incompatible with bukkit4fabric

Close due to not having complete information to diagnose the issue.