Direct answer

A mismatched mod list usually means the client and server disagree on required mod IDs, versions or their loader. Check the full list instead of copying individual files at random.

What it means

Some mods are client-only or server-only; others are required on both sides. The correct comparison depends on which mod declares the dependency and the exact pack manifest.

If you are a player

  • Use the server’s published modpack profile and exact loader version.
  • Save the full error screen and verify that a clean profile can join before installing optional client mods.

If you run the server

  1. Compare mod IDs and versions against the documented server pack, not just filename similarity.
  2. Remove accidental duplicate JARs and mods built for a different loader in a staging copy.
  3. If the host updated the pack, publish an updated client pack and restart the server after the matching change.
  4. Check server logs for the first named required mod; later disconnect lines often only repeat the same underlying mismatch.

Confirm the fix: After resolving the mismatch, test a player join and a short gameplay session; maintain the exact working manifest for future updates.

References

Use the documentation for the exact software and release you run. These sources support the settings or diagnostic behavior used in this fix.

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