unable to sync model or collection

[tohash]

 class Entities.Customers extends Backbone.PubNub.Collection                                      
      paramRoot: 'customer'
      model:  Entities.Customer                                                                  
      url:  'api/customers'                                                                    
      name:  'mopaca:customers' 

customers = new Entities.Customers

customers.fetch() //throws 'Could not sync: undefined is not a function'

/* console output
*  read 
*  Customers {length: 0, models: Array[0], _byId: Object, uuid: "b9dd7e17-1fa0-4141-9920-*  450c9637d29c", channel: "backbone-collection-mopaca:customers"…}
*
*  Object {parse: true, success: function, error: function, beforeSend: function, complete: * function}
*  function e(a){return Hb(a)} pubnub.backbone.js?body=1:90
* Could not sync: undefined is not a function 
* undefined
*/