Not receiving IOS ANCS notifications on Android

Question

We have an Android device which act as both bluetooth sync and the bluetooth peripheral. When we connect our Android device as a central with IOS ANCS for getting IOS notifications, as the ANCS charcteristic is encrypted,to write to the charcteristic we have to pair the IOS device with bluetooth. Now if the IOS is already connected with my Android device over bluetooth before connecting to IOS ANCS, then we are not able to write to the IOS ANCS descriptor,hence not getting IOS notifications.

 @Override
    public void onDescriptorWrite(final BluetoothGatt gatt, final BluetoothGattDescriptor descriptor, int status) {
        Log.d(TAG_LOG, " onDescriptorWrite:: " + status);
        // Notification source
        if (status == BluetoothGatt.GATT_SUCCESS) {
            Log.d(TAG_LOG, "status: write success is_subscribed_characteristics: "+is_subscribed_characteristics);

            if (!is_subscribed_characteristics) {
                //subscribe characteristic notification characteristic
                BluetoothGattService service = gatt.getService(UUID.fromString(service_ancs));
                BluetoothGattCharacteristic characteristic = service.getCharacteristic(UUID.fromString(characteristics_notification_source));
                notificationSourece=characteristic;
                if (characteristic == null) {
                    Log.d(TAG_LOG, " cant find chara");
                } else {
                    Log.d(TAG_LOG, " ** find chara :: " + characteristic.getUuid());
                    if (characteristics_notification_source.equals(characteristic.getUuid().toString())) {
                        Log.d(TAG_LOG, " set notify:: " + characteristic.getUuid());
                        bluetooth_gatt.setCharacteristicNotification(characteristic, true);
                        BluetoothGattDescriptor notify_descriptor = characteristic.getDescriptor(
                                UUID.fromString(descriptor_config));
                        if (descriptor == null) {
                            Log.d(TAG_LOG, " ** not find desc :: " + notify_descriptor.getUuid());
                        } else {
                            Log.d(TAG_LOG, " ** find desc descriptor:: " + notify_descriptor.getUuid());
                            notify_descriptor.setValue(BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE);
                            bluetooth_gatt.writeDescriptor(notify_descriptor);
                            is_subscribed_characteristics = true;
                            BLEAdvertise.isServiceRunning=true;
                            ClusterPeripheral.Cluster_IOS_NOTIFICATION_Characterstics.setValue(1,BluetoothGattCharacteristic.FORMAT_UINT16, 0);
                            BLEAdvertise.sendNotificationToDevices(ClusterPeripheral.Cluster_IOS_NOTIFICATION_Characterstics);
                        }
                    }
                }
            } else {
                // get current time
                Log.d(TAG_LOG, ":get time+_=-=_=-+-+-+-=_=_=_+-=-=-=-=");
                BluetoothGattService _service = gatt.getService(UUID.fromString(service_cts));
                if (_service == null) {
                    Log.d(TAG_LOG, "cant find service");
                } else {
                    Log.d(TAG_LOG, "find service");
                    Log.d(TAG_LOG, String.valueOf(bluetooth_gatt.getServices()));

                    // subscribe data source characteristic
                    BluetoothGattCharacteristic data_characteristic = _service.getCharacteristic(UUID.fromString(characteristics_current_time));

                    if (data_characteristic == null) {
                        Log.d(TAG_LOG, "cant find data source chara");
                    } else {
                        Log.d(TAG_LOG, "find data source chara :: " + data_characteristic.getUuid());
                        gatt.readCharacteristic(data_characteristic);
                    }
                }
            }
        } else if (status == BluetoothGatt.GATT_WRITE_NOT_PERMITTED) {
            Log.d(TAG_LOG, "status: write not permitted");

            //remove authrization
            Method method = null;
            try {
                method = gatt.getDevice().getClass().getMethod("removeBond", (Class[]) null);
                method.invoke(gatt.getDevice(), (Object[]) null);
            } catch (Exception e) {
                e.printStackTrace();
            }
            gatt.disconnect();

            Log.d(TAG_LOG, "onDisconnect: ");

            if (api_level >= 21) {
                if (le_scanner != null) {
                    Log.d(TAG_LOG, "status: ble reset");
                    stop_le_scanner();
                }
            }
            if (bluetooth_gatt != null) {
                bluetooth_gatt.disconnect();
                bluetooth_gatt.close();
                bluetooth_gatt = null;
            }
            if (bluetooth_adapter != null) {
                bluetooth_adapter = null;
            }
            is_connect = false;
            is_subscribed_characteristics = false;
            is_time = false;


            // Initializes a Bluetooth adapter.  For API level 18 and above, get a reference to
            // BluetoothAdapter through BluetoothManager.
            final BluetoothManager bluetoothManager =
                    (BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE);
            bluetooth_adapter = bluetoothManager.getAdapter();

            // Checks if Bluetooth is supported on the device.
            if (bluetooth_adapter == null) {
                Log.d(TAG_LOG, "ble adapter is null");
                return;
            }

            Log.d(TAG_LOG, "start BLE scan");
            if (api_level >= 21) {
                start_le_scanner();
            } else {
                bluetooth_adapter.startLeScan(le_scan_callback);
            }
        }
    }