Filtering objects by key/value in "extra" property

googlyeyes

 I'm having some trouble with the "extra" property

 I'm unable to filter objects using the key/values within "extra"

For example filtering out the places within a specific category  ==>  extra: { category: "traffic"   }

This is not working for me:

layer_id=43fu&limit=10000&offset=0&latitude=25.033611&longitude=121.565000&distance=500.000000&category="traffic" 

Any ideas?