Hi @Packrattler! Thanks for posting.
Are you attempting to activate Pandora on a device?
The Device Activation tab is for activating your Pandora account on in-home devices such as Smart TVs, Blu-ray players, etc. These devices generate codes that need to be entered on a separate device for activation.
If you're attempting to activate Pandora on your mobile device, you already have simply by signing into the app with your Pandora account email address and password.
Let me know!