I uploaded a video, but it plays upside down

It is highly likely that the video in question was recorded using an iPhone device. If this is indeed the case, it is necessary to rotate the video on the phone before exporting it. To accomplish this, please refer to the official documentation provided by Apple at the following link: https://discussions.apple.com/thread/3501039.

Alternatively, another viable solution would be to convert the video format to MP4, which should resolve the issue as well.