fetch/possible-values: how to supply path?

I'd like to be able to use imcljs.fetch/possible-values to explore the database and auto-generate a parser grammar. Digging into the source, I can't really reason about the format expected for the _path_ argument ("organism.name"?). Everything I've tried results in a 400 error ("error": "Missing parameter: 'path'). I haven't quite been able to diagnose the exact issue (in io/get-body-wrapper- I believe), but I have re-implemented the function myself using clj-http.