Minecraft Version

1.21.x

(Neo)Forge Version

21.1.59

Vampirism Version

1.21.1

Modpack

No response

Singleplayer/Multiplayer

Server

What happened?

I keep trying to run vampirism on my server and whenever I try to join it says that: channel name (vampirism: sundamage) failed to connect: This channel is missing on the server side, but required on the client!

I've tried to fix it myself but I've gotten no where

Relevant log output

No response

Reproduce steps

1. Install the Craftoria modpack
2. add vampirism to the pack
3. try to load into the server.

Other relevant mods

No response

Yes identical versions installed on both, it's the 1.10.0 beta.2 for neoforge

Just to confirm, do you have the identical Vampirism Jar installed on both server and client?
And what is the exact Vampirism version? You specified 1.21.1, but there should be more like 1.10.?-beta.?

Is vampirism more like a plugin rather than a mod?

Vampirism is a mod

I was just thinking if the server were treating it like a plugin that might be it

A quick test with just Vampirism and in Dev environment did not reproduce the issue.
I did not have time to further investigate it today

The sundamage package was marked registered to the configuration and play channel, although it only needed to be registered to the play channel. This fixes it, but it do not know why this should pose an issue here. It seems like there, it looks to me like there is not everything correct with the server.
But it is fixed for now.