Mismatched Mod Versions
Players are disconnected when joining, or the connection is refused, because the client and server are not running the same set of mods at the same versions. The world is fine, the two sides simply do not agree on the mod list.
What does this error mean?
Modded Minecraft negotiates a 'mod channel' when a client connects. If the client is missing a mod, has an extra one, or runs a different version than the server, the handshake fails and you see an invalid-channel or mismatched-mod disconnect.
Received invalid mod channel
Most Common Causes
- Client and server run different versions of the same mod.
- A required server-side mod is missing from the client (or vice versa).
- Extra mods on one side that the other does not have.
- Different loader builds (Forge/NeoForge/Fabric) between the two sides.
- A modpack updated on one side but not the other.
How To Diagnose
- Read the disconnect screen, it usually lists which mods are missing or mismatched.
- Compare the client and server mods folders side by side.
- Verify both use the identical modpack version.
- Confirm both run the same loader and Minecraft version.
Recommended Fixes
- Sync the modpack exactly
Install the same pack version on client and server so every mod and version matches. - Align individual mods
For manual setups, copy the exact jars between client and server. - Separate client/server-only mods
Keep client-only mods off the server and server-only mods off the client, but match everything else. - Update both sides together
When you upgrade the pack, upgrade the server and every player at the same time.
Frequently Asked Questions
Gameplay mods must match. Purely client-side mods (minimaps, shaders) usually do not and should not be on the server.
Distribute the modpack file or a zipped mods folder so everyone runs identical jars.
Those players already have the matching version. Others are on an older or different build.