This command is separate from the Discord Auth /auth command. Setting up that one does not set up this one.
To set up raid notifications, type in chat: /rn discord "<your discord name and #>"
Notice the double quotes. You MUST include them, especially if you have a space in your name.
So for example, if I were to set up raid notifications for myself, I would type: /rn discord "LazySl0b#9015"