It's possible the video is not supported by your current media player. In that case, you should use your device's default video player.
The video may also get removed by accident, which may happen when a video that's not been loaded properly is saved in the editor. This can result in the final download appearing as an image file rather than a video.
If this is the case, the first step is to duplicate your design. Your design can be duplicated by opening in the editor, click 'Duplicate Design' from 'File'.
In the copied design, add your video, save and make sure the video is present prior to purchasing.
Report your previous purchase so we can refund it as soon as possible.