Roku does have a warning on their website about this scam and it doesn't just happen with Roku, but any company that requires an activation as it's very easy for scammers to create copycat websites.

Enter the code found on the Activation screen on your device. Leave your device connected and on the activation code screen. Verification of your TV service provider is handled by your TV service ...

Along with the support for buying via the Roku app, the update also includes a handful of other improvements, like the ability to use activation codes instead of signing in with an email and ...