Unable to get BrowserPrint to work

I am using this code. It seems to send something to the printing, but nothing is happening.

// BrowserPrint for Zebra Printer

BrowserPrint.getDefaultDevice('printer', function(printer) {

        if((printer != null) && (printer.connection != undefined)) {

            console.log('Using print '+printer.name);

            //printer.send(format_start + txtToPrint + format_end);

            printer.sendUrl(

            'http://domain.com/my-document', // my url is behind a network

            function(success_response) {

            console.log(success_response);

            },

            function(error_response) {

            console.log(error_response);

            },

            );

        } else {

          alert("No Printer Found");

        }

  },

    function(error_response) {

  // This alert doesn't pop either

  alert(    "An error occured while attempting to connect to your Zebra Printer. " +

                "You may not have Zebra Browser Print installed, or it may not be running. " +

                "Install Zebra Browser Print, or start the Zebra Browser Print Service, and try again.");

    }

);

});


The Demo works, using a printer different from the one I have installed. It is called 29j152601705, rather than Zebra GK420t.

I am not sure what I am doing wrong or how to debug this.