Picture wil not be shown when shared in facebook

The picture of the article will not be shown, wenn article is shared in facebook. Text is shown.
The facebook debugger says: missing: fb:app_id

Maybe this is the problem, but what ist the app_id and how do I get it?

Shared Link:
http://www.balticsoft.de/blog/rechnungsprogramm-fuer-kleinunternehmer.html