Greetings, lonskis1!
Thanks for reaching out in Apple Support Communities! If we understand correctly, you've rented a movie from the iTunes Store and it can't be downloaded on your iPad.
Check this out: Rent movies from the Apple TV app. It goes over the process on how to rent the movie using the Apple TV app. Also, there are suggestions included in the "Get help" section including how to report this as a problem.
You've mentioned that it's almost finished downloading then stops, you'd want to make sure you have enough storage on your iPad as something you can check. You might even want to sign out, then sign back in the Apple TV app to see if this gets the download to complete.
Let us know if this helped.