'Database error' message when sharing my latest post on Facebook

When I try to share my latest post to Facebook, instead of the usual picture and 100 or so words showing it says ‘database error’, even though the link itself is good.

This is the latest post and the one I am having this issue with. Older posts are fine.
https://www.glenysnellist.com/?p=2019

I went to the Facebook Debugger and scraped my site. It tells me in the Warnings That Need To Be Fixed area:

Share App ID Missing
The ‘fb:app_id’ property should be explicitly provided, Specify the app ID so that stories shared to Facebook will be properly attributed to the app. Alternatively, app_id can be set in url when open the share dialog.

I am at a complete loss, and don’t know how to do this. Please help!