Fix startup failures
Identify the failing stage before replacing files or removing worlds.
On this page
Java or version mismatch
Run java -version in the actual launcher/panel environment. Target Java 21 and Minecraft 1.21.11. If UnsupportedClassVersionError names a plugin, check its Java requirement too. Your personal terminal does not select a container runtime. See Java installation.
Paperclip or EULA
For incomplete runtime downloads, check outbound access, storage, permissions, and the download error. Do not repeatedly kill a process still making progress. If stopped at EULA, the owner must read and agree to the Minecraft EULA before editing the acceptance file and restarting.
Licensing may stop earlier, before later world/config files exist. Follow license setup rather than deleting unrelated files.
Port already in use
Check for an older process or another service using the same port. Match server-port, bind address, and panel allocation. Stop a process through its owning console/service rather than killing unrelated processes. See connection checks.
Invalid configuration
Stop and retain a private copy of the failing file. Check spaces/indentation, duplicate keys, boolean types, uppercase mode values, and numeric bounds. Quoted false is a string. Resume TPS cannot be below minimum TPS; total deferred redstone cannot be below the per-chunk bound.
Restore the last known-good file and restart fully. Do not share raw parser dumps containing private values. Plugin reload does not apply Nusa startup settings.
World will not load
Do not overwrite the old world with a new one. Record its version, relevant redacted error, permissions, disk availability, and possible process locks.
Worlds saved with Nusa zstd need a compatible reader or pre-migration backup. Do not open the only copy in unmodified Paper. Follow world rollback on a copy.
License verification fails
Check key-source priority, system time, and outbound HTTPS. A dashboard token is not a license key. Correct key syntax does not prove signed authorization succeeded. Use the customer channel with a redacted report if the issue persists.