Unable to purchase a movie on Apple TV

I was gifted a movie through Amazon Prime video but would like to purchase it through Apple TV in order to get the iTunes Extras. While I can see the price of the movie, there is no option to buy it. The only option is to Play, indicating that it's from Prime Video. I tried disconnecting the PV app on my Apple TV account, but that doesn't work. I also tried purchasing directly from iTunes store, but can't do that either. Does anyone know a work-around?