This widget will display a Responsive YouTube or Vimeo video in pages / posts and sidebars.
Make sure you have copied the main URL from your address bar for the video and not the supplied embed code
Make sure you have selected the correct video type. If Vimeo is selected but a YouTube URL is pasted (or vice versa), it will not work
If this is a Vimeo video, ensure you have permission for the video to be embeded on your domain. You may have to contact the video owner to get this.
Make sure that the
div> that contains the video has a width set and that it is a percentage and not a fixed width.