Custom dimensions aren't recognized on servers

Custom dimensions work fine on singleplayer and LAN worlds, but on servers, it doesn't recognize them.

What I expected to happen was...:
I typed /execute in [namespaced ID] run tp @s ~ ~ ~ in the chat, and I expected to be teleported to the custom dimension, which is exactly what happened when I did it in a singleplayer world and a multiplayer LAN world.

What actually happened was...:
On the server though, I just got an error message saying "Unknown dimension". I checked the log file but it didn't indicate that anything was wrong when I reloaded after installing the datapack.

Steps to Reproduce:

1. Add a datapack with a custom dimension to the server's world
2. Reload the server
3. Join the server and type /execute in [namespaced ID] run tp @s ~ ~ ~ and you'll get the same error message
4. Do the exact same thing in a singleplayer world or a LAN world and it'll work just fine. It's only a problem on servers for some reason