Video does not play when clicking the button

Hi, I just installed the plugin and did the configurations. The video is shown instead of the feat. image – that’s fine. But when I press the play button on the video nothing happens. The only think I can do is to activate the auto-play which I do not want to use as you cannot stop it. Did anyone have this problem before that you cannot watch the video you put as a featured video and could solve it? Thank you very much for your help!