AngularJS UI Bootstrap typeahead with ajax using Coffeescript

My question is very similar to this post 'Using typeahead and ajax in a AngularJS app'

Coffeescript:

  $scope.tradingPartners = (searchOn) ->
    console.log("Searching on #{searchOn}")
    $.getJSON("../tp/tpLookupAdmin", {term: searchOn, max: 20}, (response)->
        response)

Generates Javascript:

$scope.tradingPartners = function(searchOn) {
      console.log("Searching on " + searchOn);
      return $.getJSON("../tp/tpLookupAdmin", {
        term: searchOn,
        max: 20
      }, function(response) {
        return response;
      });
    };

Using it:

<input type="text" ng-model="testScript.sender" typeahead="sender as sender.label for sender in tradingPartners($viewValue)" 

So whats wrong? ...

The getJSON call is made just fine, the results look good but the typeahead does not do anything. If I put hardcoded values in as the return from the function it works just fine.

Now I know the getJSON is not just returning an object array, and doing

$.getJSON("../tp/tpLookupAdmin", {term: searchOn, max: 20}, (response)->
        response).responseJSON

gives undefined.

Example hardcoded json that works:

[{"id":"1","label":"test1"},{"id":"2","label":"test2"}]

I'm missing something simple here...