Sends wrong image

I tested it by sharing an image to a Facebook page for my website. When the box popped up, it showed the image I intended to share. When I checked Facebook, it was using the featured image for the page instead of the selected image. If you want people to share your featured images, this may be worthwhile. But I use the featured image for related posts, and I keep it at a certain size. To advertise a page on Facebook, I want to use a larger, more informative image that is customized for social media.