Error while trying to play a video on my iPhone

7Tariq wrote:

This video is very important to me. How can I open it please?

There are probably at least a dozen reasons you are seeing that message. Without much more information it is impossible to tell you why you have the issue.

No idea without more information. From where did you get this video or on what site are you trying to view it. And with what app, on what device (model and version of iOS/iPadOS, as applicable)?