The same thing is happening to me. I bought the Inteset IReTV USB IR Receiver & USB Y Cable with The Inteset INT422 & Harmony Remotes, and I'm using the Xbox 360 codes, but nothing works when I press the buttons on the remote. I have a MX-990 remote.

I even have the MRF 350/MRF-260 sensor on the Inteset IR receiver and the blue light comes on when I press a button on the remote. In fact, both sensors light up, but it's not controlling any functions for the Firestick. I have a Firestick 4K Max. Can someone please help?

Thank you in advance for your assistance!