On Sony TV, Android TV/Google TV, Fire TV, it is currently not supported to do in-app financial transactions in the Apple TV app. Instead, try subscribing (or buying, or renting) on a different supported device(*). Once the transaction is done, then you will be able to access the purchased service in the Apple TV app on Sony TV, as synced through the use of the matching Apple ID account.
Support article 102472 [footnote 2]:
2. In the US, you can subscribe to Apple TV+ on Amazon Fire TV, but you can't purchase other content from the Apple TV app. On Amazon Fire TV (in other regions), 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.
(*) Supported devices for financial transactions are: iPhone, iPad, iPod touch, Mac, Vision Pro, Windows PC with Apple TV app, Roku, LG TV, Samsung TV, Vizio TV, PlayStation, Xbox. Users can also subscribe to (just) Apple TV+ on the web (on computers), at tv.apple.com.