A command you know exists comes back as unknown. Nine times out of ten the plugin is loaded and working, and the server is hiding the command from you because you do not have permission to use it.
Why it happens
The server does not distinguish between a command that does not exist and a command you are not allowed to run — it says «unknown» for both, deliberately, so that a lack of permission does not reveal what a server has installed. That is a sensible design and it is also why this is the most misread message in Minecraft.
What to do
- Check the plugin actually loaded
/pluginslists them, green for loaded. If yours is red or missing, this is a loading problem and the console will say why. - Try the command as an operator
If it works with op and not without, it is permissions — which is the answer nine times out of ten and takes ten seconds to establish.
- Find the exact permission node
The plugin's documentation or its
plugin.ymllists them. Guessing at node names is the slow way. - Check the node is granted in the right context
Permissions plugins support per-world and per-server rules. A node granted in the wrong context is set and inactive at the same time, which is genuinely confusing to look at.
- Try the fully-qualified name
/pluginname:commandbypasses any conflict over the short name. If that works and the short one does not, another plugin has claimed it.
Operators bypass most permission checks, so every command works for you and nothing works for anyone else. Testing with a second, unprivileged account is the only way to see what your players actually experience.
/help and tab completion only show what you may useThat makes them a fast permission test. If a command does not appear when a player presses tab, they do not have it — no need to have them type anything.
A player in the intended group runs the command successfully, and a player outside that group still cannot see it.