Control MagicBlue ble light bulb doesn't work

Hello!

I am trying without success since couple hours to make work a simple system: button press turns on a light bulb.

Regarding the reverse engineering of the bulb https://medium.com/@urish/reverse-engineering-a-bluetooth-lightbulb-56580fcb7546

I managed to control the bulb from a Cordova app, so the javascript should already be ready. I manage to connect to the device, to get the service and characteristic I need...but cannot make it to writeValue correctly (the bulb is not reacting). No error is thrown.

I suppose the problem hides in the value passed - in Cordova through I library should be an ArrayBuffer - but here?

My code

  LED1.write(false);
  LED2.write(false);
var connected = false;

setWatch(function() {
//  NRF.findDevices(function(ds){
  //console.log(ds);
   if(!connected){ connecty();}
    else{console.log('already connected');}
  //},1000);
}, BTN, {edge:"rising", debounce:50, repeat:true});


function connecty() {
  var gatt;
  NRF.connect("c9:a2:57:28:a3:15 random").then(function(g) {
    connected=true;
    LED2.write(true);
    gatt = g;
    return gatt.getPrimaryService("0000ffe5-0000-1000-8000-00805f9b34fb");
  }).then(function(service) {
    return service.getCharacteristic("0000ffe9-0000-1000-8000-00805f9b34fb");
  }).then(function(chara) {
    LED3.write(true);
    chara.writeValue(makearr());
  }).then(function(a) {
    gatt.disconnect();
    connected=false;
    setTimeout(function(){
      LED2.write();
    LED3.write();},1000);
    console.log("Done!");
  }).catch(function(e){
  console.log('error');
    connected=false;
  });
}


function makearr(){
  var hex = 'ff085a';
 //'02','40','00','0e','00','0a','00','04','00',
  var arra = ['56',hex.substr(0,2),hex.substr(2,2),hex.substr(4,2),'00','f0','aa'];
  var bf = new Uint8Array(arra.length);
  for (var y in arra){
    bf[y]='0x'+arra[y];
  } 
  return bf.buffer;
}

Any suggestion will be very appreciated!