Direct answer
Open logs/latest.log, go to the startup section where the plugin is loaded, and read the first exception/message for that plugin. The most common fixes are installing a required dependency, using a plugin build compatible with your Minecraft/Paper version, replacing a corrupt/wrong JAR, or removing a duplicate copy.
Diagnosis to use: The first startup exception determines whether a plugin has a missing dependency, incompatible API, bad JAR or configuration error.
Confirm Paper is even trying to load the file
Paper loads plugin .jar files from the root of the plugins directory. A JAR inside a subfolder, a ZIP you forgot to extract, or a Forge/Fabric mod will not behave like a normal Paper plugin.
What to collect: Read logs/latest.log from the beginning of that plugin’s enable attempt and the first “Caused by” line. Compare api-version requirements and depend entries against your installed server build and companion plugins.
Check /plugins after a full restart
A plugin shown in red is present but not enabled. Do a full stop/start after plugin changes; avoid using the general /reload workflow as a substitute for a clean restart.
Match the first error to the specific fix
UnknownDependencyException: install/update the named dependency.Unsupported API version: the plugin declares a newer API than the server supports.Invalid plugin.yml: wrong artifact, broken/incomplete download, or invalid plugin package.Ambiguous plugin name: two JARs declare the same plugin name.NoSuchMethodError/NoClassDefFoundError: often a plugin/library/server compatibility problem; verify the exact supported versions.
Targeted repair: Install the correct platform-specific release and required dependencies. Do not delete the entire plugin data folder unless the vendor specifically documents that as a migration step.
Verify after the change: Restart rather than hot-reloading after JAR changes, then test a real non-operator feature and confirm its enable message.
If you still cannot identify the plugin
On a backup/test copy, remove all plugins and add them back in groups using a binary-search approach. Paper explicitly recommends this for plugin-induced issues and notes that dependencies should stay grouped together.
Official references
These references were checked while preparing this fix. Version-specific behavior can change, so use the project documentation for your exact release when a detail differs.
Related fixes and guides
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