"Could not load command ... Illegal Characters"

Server log

Could not load command shop:open for plugin MyPlugin: Illegal Characters

What it means

The plugin loads, but this command (or alias, in "Could not load alias ...") is skipped. Players cannot use it.

What causes it

The command or alias name contains :. The colon is reserved for the plugin:command form that the server creates on its own.

How to fix it

Before

commands:
  shop:open:
    description: Opens the shop

After

commands:
  shop:
    description: Opens the shop
    usage: /shop open

Handle open as an argument in your command code. Players can already type /myplugin:shop to reach your command when another plugin uses the same name.

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