IPhone 4 movie won't download?

I have an iPhone 4 if that helps but I just ordered a movie from iTunes and in order to download it you have to have a lot of space on it. I have more storage than it needs and it keeps saying to manage my settings and that it won't download. Anyone know what's going in? If so can you please help?

Because if there's a bug in your download app you have no choiceto wait to be resolved like you would android by having a choice of dozens of downloaded apps…