Unknown or incomplete command

I have:

forge-1.20.1-47.4.1-installer.jar

forge-1.20.1-47.4.1-installer.jar

forge-1.20.1-47.4.1-installer.jar

forge-1.20.1-47.4.1-installer.jar

DistantHorizons-2.3.4-b-1.20.1-fabric-forge.jar

DistantHorizons-2.3.4-b-1.20.1-fabric-forge.jar

DistantHorizons-2.3.4-b-1.20.1-fabric-forge.jar

DistantHorizons-2.3.4-b-1.20.1-fabric-forge.jar

When I join the server chat says:

Distant Horizons: Alex's Cave detected.
You may have to change Alex's config for DH to render.

Typing

/dh

/dh

/dh

/dh commands on the server console or in-game with an op account say

Unknown or incomplete command

The Distant Horizons options do show up in the pause menu.

MODS

I'm using Beyond Depth modpack, plus: