Solution: You can reset the FB cache here:
https://developers.facebook.com/tools/debug/?hc_location=ufi
Related: http://ogp.me/
Error: App Id Missing
developers.facebook.com is a valuable tool. I got the error, that the app id was missing. The solution is to create an app in the Facebook Developer. Use the id from the app in the markup, e.g.
<meta property="fb:app_id" content="123456789012345">