I just joined Apple TV+ to watch a movie supported by Apple. It's called "Drunken birds".
Drunken Birds (2021) on iTunes - Apple (CA)
You don’t need an Apple TV+ subscription to order this movie from the Apple iTunes Store (Canada). The movie is not part of the Apple TV+ catalog [1] [2], but instead part of the iTunes Store movies catalog [3] (buy or rent). It is the same for subscribers and non-subscribers. You can order it with an Apple ID account and a linked payment method. After ordering the movie, you can watch it in the Apple TV app on your Fire TV device or any other device with the Apple TV app. However, you can’t currently make the purchase on Fire TV.
I see it's there but when I click on it to watch it, it says that I can buy, rent or subscribe in the Apple TV app (but am I not alresdy in the app??!!)... I'm lost! Help^!
Unfortunately, in-app purchases aren’t supported at this time in the Apple TV app on Fire TV devices.
From: https://support.apple.com/kb/HT209440: “Need help? 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.”
So please make the financial transaction on a different device. If you do not have device that supports in-app transactions for Apple digital purchases (e.g. iPhone), then consider using the iTunes application for Windows to do so.