Please Help me this function doesn't fire from the periperical?

Official Hardware Nano Family Nano 33 IoT
7

yes the central is and android app.

#include <ArduinoBLE.h>

BLEService ledService("77B10000-E8F2-537F-4F6C-D104768A1777"); // BLE LED Service

// BLE LED Switch Characteristic - custom 128-bit UUID, read and writable by central
BLEByteCharacteristic switchCharacteristic("77B10001-E8F2-537F-4F6C-D104768A1777", BLERead | BLEWrite);

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

void setup() {
  
  Serial.begin(9600);
  while (!Serial);

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

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

    while (1);
  }

  BLE.setLocalName("xxxxxx");
  BLE.setDeviceName("xxxxxx");

  String address    = BLE.address();


  BLE.setAdvertisedService(ledService);

  // add the characteristic to the service
  ledService.addCharacteristic(switchCharacteristic);

  // add service
  BLE.addService(ledService);

  // set the initial value for the characeristic:
  switchCharacteristic.writeValue(0);

  // start advertising
  BLE.advertise();

  Serial.println("xxxxxx visible...");

}

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:
    Serial.println(central.address());

    if(central.hasLocalName()){
      Serial.print("Connected to central: ");
      Serial.println(central.localName());
      
    }

    // 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()) {
        int value  = switchCharacteristic.value();
        Serial.print("value: "+value);
        if (value ==1) {   // 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
        }
      }else{
         //Serial.println("is connected:"+central.address());
      }
      //delay(1000);
    }

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

please get me this libray please...