printing bill takes so much time in sunmi v2 device flutter app

Question

I have a flutter application, in which I print bill it takes approximately 30 seconds, what is the reason please?!

when user clicks on the button, the onpressed is like this:

      onPressed: () {
        controller.capture(delay: const Duration(milliseconds: 10)).then((capturedImage) async {
          Get.back();
          onPrint(i.decodeImage(capturedImage!));
        }).catchError((onError) {
        });
      }