Facebook cover art is not showing up

Facebook requests the image from your cover art within a few minutes of the first time a link is posted. The first time a link is posted it will be missing for a few minutes.

If you paste your link here: https://developers.facebook.com/tools/debug/ - That page will force the image to update on Facebook (if you don't want to wait). So if the image is black this will fix it faster than waiting 1-2 minutes.