Nearly all customer issues with ZIP files are caused by incomplete downloads.
You're probably anxious to watch your new video or try out your new BlendKit but be patient and give it time to get to you. Our product files may be much larger than you're used to and some products, such as our 10K textures, are over 800MB in size. This can take a bit of time, even with a fast connection. So keep an eye on the download progress bar and only unzip the file once the transfer has completed.
Double-click to unzip the downloaded file.