The Amazon Fire TV Game Controller was released to allow you to play games on your various Fire TV devices, making the smart streaming line of devices a bit smarter and a bit more useful. Though the games you could play were nothing more than Android games, some saw a use for the controller.
Unfortunately, Amazon doesn’t intend to support it anymore. The updated page for the controller now states that it isn’t compatible with the Fire TV with 4K Ultra HD, Fire TV Edition smart TVs, or Fire Cube. It is still compatible with the Fire TV Stick at the moment. This is due to a software update removing support, so your controller that worked previously may no longer work.
This is the kind of thing that happens when a company uses proprietary connection methods. Though Bluetooth was used on the first generation controller, Amazon switched to WiFi for the second generation for better latency and range. The WiFi protocol used here is no longer being supported and your controller is likely useless.
You can still use a Bluetooth controller, but we doubt that many people play games on their Fire TV devices anyway. If you do, pick up a PS4 or Xbox One controller for the Bluetooth support.