Direct answer

Java rejected a JVM flag before Minecraft started. Remove or replace the exact unsupported/typoed option, then verify the Java version used by the startup environment. Do not copy old flag packs across Java versions blindly.

What it means

A JVM flag in the startup command is not supported by the Java runtime that actually launched.

If you are a player

  • This is a server-side startup problem. Send the owner the exact panel/console error; reinstalling your game client will not fix it.

If you run the server

  1. Read the first Java/JVM error before the final “server stopped” or panel exit-code summary.
  2. Run java -version in the same shell/container/panel runtime that actually launches the server.
  3. Verify the Java release and JVM arguments against the exact server software/version; remove old or copied flags that the current runtime rejects.
  4. Fix startup/runtime selection before changing world or plugin data, because Minecraft may not have started yet.

Current Paper Java requirements

Paper currently documents Java 21 for Paper 1.20 through 1.21.11 and Java 25 for Paper 26.1+. Other server software or older Minecraft versions can require a different Java release, so check that project’s exact version table.

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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