Apple tv app

"ways to watch"

• Currently the Apple TV app on Fire TV doesn’t support in-app purchases [2]. Any subscribing/​buying/​renting will have to be done on a different device. Once the transaction is complete, then you can view it on Fire TV or any of your other devices with the Apple TV app.
• This restriction wouldn’t apply to the Apple TV app on supported Samsung models. Users can subscribe/​buy/​rent on there.

Get the Apple TV app or Apple TV+ app on your smart TV, streaming device, or game console - Apple Support

2. On Amazon Fire TV, Android TV, and Sony TV devices, you can't purchase content from the Apple TV app. You can buy, rent, or subscribe on another supported device and then watch in the Apple TV app on your Amazon Fire TV, Android TV, or Sony TV device.

It sounds like whatever you are trying to watch isn't available on AppleTV+. "Ways to Watch" tells you how you can watch it elsewhere, including third-party services and buying it directly from Apple.

Please provide more information so that we can help you. Which device are you trying to use the AppleTV app on? What happens when you try to watch a movie?