encode does not execute success or fail

[widonwaker]

cordova.plugins.barcodeScanner.encode(cordova.plugins.barcodeScanner.Encode.TEXT_TYPE, "http://www.nytimes.com", function(success) {
alert(success);
}, function(fail) {
alert(fail);
}
);

as in the example, the qr code is correctly generated but I do not have chance to manage the success or fail functions. Alert not triggerins and so I cannot manage the scan via javascript.