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+[⬅️ Back to `index`](index.md)
+
+# Not Found
+
+The Not Found reply (421) is when the server doesn't recognise a command a client sends.
+
+Say the person executing the unknown command has the nickname `nick`
+```
+↗️ UNKNOWNCMD :something
+↙️ :server 421 nick UNKNOWNCMD :Unknown command
+```
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