BULK Lead Extract - Retrieve Data File returns blank

[Anonymous]

Hello, need some direction with Retrieve Data file as I'm not seeing any data in the results file:

here is what I'm trying to bulk extract from Leads:

{

   "fields": [

      "firstName",

      "lastName",

      "email"

   ],

   "format": "CSV",

   "columnHeaderNames": {

      "firstName": "First Name",

      "lastName": "Last Name",

      "email": "Email Address"

   },

   "filter": {

      "createdAt": {

         "startAt": "2017-10-01T00:00:00Z",

         "endAt": "2017-10-31T00:00:00Z"

      }

   }

}

The Status is Completed and there is data for the startAt and endAt dates queried above....

Yet the Retrieve API job returns a blank. using content-type=application/json after trying application/x-www-form-urlencoded - made no difference..got no results. What am I missing here.

Any pointers will be helpful

thanks in advance!