Charles Buchwald

Muddling my way through Advanced Custom Fields. I don’t actually have a thumbnail… just a link. But that will do for now.
I figure since I only have about 5 file types, that later I can show a “generic” thumbnail for each type.

Figured it out myself! I am using a custom post type with a custom field for file uploads, and I was trying to display the non-custom file thumbnail… which of course does not exist.
Once I realized this, and used the proper (custom) field name, it displays just fine.