https://techcrunch.com/2017/08/22/walmarts-streaming-service-vudu-hits-apple-tv/

As reported earlier this month, Walmart’s streaming service Vudu has now arrived on Apple TV… with a few limitations. The new app allows you to watch the movies and shows saved to your Vudu library, including those you’ve added by way of UltraViolet, the digital video “cloud locker” technology that lets you watch digital versions of your DVDs and Blu-rays. However, like its iOS counterpart, the Apple TV version of Vudu doesn’t allow you to rent or buy videos through the app directly.

Instead, if you want to make a purchase, you have to do so through the browser or another device first. This same limitation is found in Vudu competitor, Amazon Video, which is currently only available on iOS, in terms of Apple device support outside the browser.