An Apple TV Watchlist entry is not a purchase
Use the Watchlist, Library and title page to tell saved films from films you already bought.
IPTVBlogs editorial desk · 
Apple’s Watchlist stores titles you want to find again. To confirm whether you bought or rented a film, check the Library under the Apple Account associated with the transaction and then open the exact title page.
Find the source behind the saved card
The Watchlist can help you return to a title after you see a trailer. At viewing time, open its details and read the access label. If it points to another service, check that app and account before assuming that Apple will play it as part of your subscription.
Check the edition and purchase account
If the Library and Watchlist show similar cards, compare the title year and edition. Find the receipt before paying again. An item may be saved in one app profile while the purchase belongs to another Apple Account in the same household.