Hello TR73,
Thanks for using the Apple Support Communities. We understand that you're having an issue with a purchased movie from iTunes not playing or downloading as expected. Can you tell us what happens with each option? If any error messages are received, let us know the details.
Would you please let use now what macOS version you have installed on your MacBook? You can locate this information by clicking the Apple Menu () in the top left corner and selecting About this Mac.
Reviewing article, If you can't stream or watch movies or TV shows from the Apple TV app, iTunes Store, or third-party apps, it mentions testing the movie on a different device. Were you able to give that a try? It can help us determine if the issue is with your MacBook or something is going on with the movie itself.
Also, were you able to try using a different network to see if the issue persists? If not, give that a try. If you can't access an alternate network, try restarting your Wi-Fi router to see if that helps.
Best regards.