MIT App not detecting Nano 33 IoT

I am currently working on a project to turn on and off the builtin LED in an Arduino nano 33 IoT. I am trying to build a mobile app to do this via bluetooth.

My app has not been able to detect any BLE devices. I'm not sure why. Please help.

The code is:

#include <ArduinoBLE.h>

BLEService ledService("19B10000-E8F2-537E-4F6C-D104768A1214"); // BLE LED Service

// BLE LED Switch Characteristic - custom 128-bit UUID, read and writable by central
BLEByteCharacteristic switchCharacteristic("19B10001-E8F2-537E-4F6C-D104768A1214", BLERead | BLEWrite);

const int ledPin = LED_BUILTIN; // pin to use for the LED

void setup() {
  while (!Serial);

  // set LED pin to output mode
  pinMode(ledPin, OUTPUT);

  // begin initialization
  if (!BLE.begin()) {
    Serial.println("starting BLE failed!");

    while (1);

  // set advertised local name and service UUID:

  // add the characteristic to the service

  // add service

  // set the initial value for the characeristic:

  // start advertising

  Serial.println("BLE LED Peripheral");

void loop() {
  // listen for BLE peripherals to connect:
  BLEDevice central = BLE.central();

  // if a central is connected to peripheral:
  if (central) {
    Serial.print("Connected to central: ");
    // print the central's MAC address:

    // while the central is still connected to peripheral:
    while (central.connected()) {
      // if the remote device wrote to the characteristic,
      // use the value to control the LED:
      if (switchCharacteristic.written()) {
        if (switchCharacteristic.value()) {   // any value other than 0
          Serial.println("LED on");
          digitalWrite(ledPin, HIGH);         // will turn the LED on
        } else {                              // a 0 value
          Serial.println(F("LED off"));
          digitalWrite(ledPin, LOW);          // will turn the LED off

    // when the central disconnects, print it out:
    Serial.print(F("Disconnected from central: "));

I've also attached a screenshot of the app.

Please let me know if any further information is required. Thanks in advance.

Can you please modify your original post to ensure the source code is in a single box. It should look like this.

// Your example source code

You need three ' at the beginning and end in the edit window? When you click on this icon </> you get.

type or paste code here

This ensures we can get all the source code. Right now if you copy the code there are invisible characters that prevent successful compilation and parts might be missing.

Did you test the sketch using a generic BLE app on your smartphone? I use BLE Scanner on iOS. There are many others on iOS and Android.

Please note, most of the example sketches require you to start the Serial Monitor. Otherwise they will be stuck at:

while (!Serial); // code will wait for Arduino IDE Serial Monitor to be opened

If you run your Arduino from a USB power pack you will need to comment or remove this line of code.

Thanks for your help, I was able to resolve this issue!