I'm not exactly sure why you're getting that error. However, it looks like you're trying to put the transformer on the query itself, and I don't think that will work.
I would recommend create the transfomer separately.
Here is a an app you can import that works for me.
test3.json (11.4 KB)
Of course, this is setup to filter against my own database, so the query and transformer would need to be updated to reference your specific data.
