SignalR doesn't reach JS client function

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C#

Javascript

SignalR

I can successfully call testFunc() on my server. But the Invoke simply never gets to my testFuncCallback() function. Since I can call the server, the connection appears to be fine.
Any idea what's going on?

[HubName("testHub")]
public class testHub: Hub
{
    public void testFunc()
    {
        Clients.Caller.Invoke("testFuncCallback");
    }
}

$scope.lTestHub = $scope.$parent.signalrConnection.testHub;
$scope.lTestHub.on('testFuncCallback', function () {
    alert("jo");
});
$scope.lTestHub.server.testFunc();