The problem with JSON files is: They are often surrounded by additional text. See this forum thread with information from Jim Rea.
Basically the part that Panorama X can work with is the array between straight brackets “[” and “]”. You need to cut away surrounding text e.g.:
{
"items":
and the curly bracket following the JSON data.
The screenshots show the QuickLook preview of an unmodified file and the contained pure JSON data.
