"Unsupported API version"

Server log

org.bukkit.plugin.InvalidPluginException: Unsupported API version 26.9

What it means

api-version is the oldest server version the plugin supports. When it is newer than the server, the server refuses the plugin.

What causes it

The plugin was built for a newer Minecraft version than the server runs, or api-version has a typo such as 26.10 instead of 26.1.

How to fix it

Before

api-version: '26.9'   # server runs 26.3

After

api-version: '26.3'

If you are a server owner, update the server or find a plugin version for your Minecraft version. If you are the developer, set api-version to the oldest version you actually support. Unquoted values are read as text in current Paper, so 26.10 stays 26.10.

Check the whole file. Paste your plugin.yml or drop the plugin jar into Permistry. It finds this and about 40 other problems, and explains each one in plain words. It runs in your browser and nothing is uploaded.

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