Sorting columns with smart table

Question

I am trying to sort columns by clicking on the header item using smart table. But it does not work for me. What am I doing wrong?

This is my HTML:

<div class="pane pane--table1" st-table="data.content" st-safe-src="data">
  <div class="pane-hScroll">
    <table>
      <thead>
        <tr>
          <th ng-repeat="item in data.header" st-sort="{{item}}">{{item}}</th>
        </tr>
      </thead>
    </table>
    <div class="pane-vScroll">
      <table>
        <tbody>
          <div ng-include="'templates/includes/ajax_spinner.html'"></div>
          <tr ng-repeat="value in data.content">
            <td ng-repeat="(key, val) in value[0]">{{val}}</td>
          </tr>
        </tbody>
      </table>
    </div>
  </div>
</div>