Zoom in a slide in a slide-box

I have created a n images gallery with the ionic slides box.
Now im trying to add a Zoom-In option by double tapping and it doesnt work.

This is my code:

<!-- Ionic header -->
<ion-header-bar align-title="left" class="bar-calm">
	<a nav-direction="back" ui-sref='album({id: aId})'>
		<button class="button button-clear icon ion-android-arrow-back">    </button>
    <h1 class="title" ng-bind="title"></h1>
<!-- End of ionic header -->

<ion-content scroll="true" zooming="true" delegate-handle="mainScroll" direction="xy">
	<!-- Ionic slide-box widget	 -->
   <ion-slide-box show-pager="false" active-slide="photoIndex" zooming="true" direction="xy" delegate-handle="imageScroll">

   		<!-- Single slide element -->
	    <ion-slide ng-repeat="photo in photos" on-double-tap="doubleTapped()">

		    <!-- Slide image wrapper -->
		    <div class="carousel-image-wrapper">
		       	 <img ng-src="{{ photoUrlPrexif + photo.url }}"> 
		    <!-- end slide image wrapper -->
	    <!-- End of single slide element -->

	<!-- End of slide-box -->

in my controller i do the following

	$scope.doubleTapped = function(){
	console.log(	$ionicScrollDelegate.$getByHandle('mainScroll'));

	$ionicScrollDelegate.zoomBy(2, true);

I get the following error:
Error: Zooming is not enabled!

But i did configure zooming="true"
How can i solve this?