didUpdateValueFor callback function of Core Bluetooth doesn't fire

Question

I am using Core Bluetooth in an iOS app using Xcode and Swift to get data from a Muse 2. The process works except the didUpdateValueFor callback function doesn't fire. The didUpdateNotificationStateFor callback function fires, and when I print the characteristics, they show that they are notifying. I have done the same thing with a Polar H10, and it works just fine.

One of the characteristics has a write without response property. What would I write to the characteristic?

Do the makers of Muse 2 Headband share information about their protocol?

import UIKit
import CoreBluetooth

class ViewController: UIViewController {

    var workerQueue = DispatchQueue(label: "us.utili.TrialMuse.workerQueue")
    var centralManager: CBCentralManager! = nil
    var muse: CBPeripheral! = nil

    override func viewDidLoad() {
        super.viewDidLoad()

        let options: [String: Any] = [CBCentralManagerOptionShowPowerAlertKey: true]

        self.centralManager = CBCentralManager(delegate: self, queue: workerQueue, options: options)
        self.centralManager.delegate = self

    }


}

extension ViewController: CBCentralManagerDelegate {

    func centralManagerDidUpdateState(_ central: CBCentralManager) {

        print("centralManagerDidUpdateState")

        switch central.state {
        case .unknown:
            print("central.state is .unknown")
        case .resetting:
            print("central.state is .resetting")
        case .unsupported:
            print("central.state is .unsupported")
        case .unauthorized:
            print("central.state is .unauthorized")
        case .poweredOff:
            print("central.state is .poweredOff")
        case .poweredOn:
            print("central.state is .poweredOn")
            centralManager.scanForPeripherals(withServices: nil)
        @unknown default:
            print("switch central.state @unknown default:")
        }

    }

    func centralManager(_ central: CBCentralManager, didDiscover peripheral: CBPeripheral, advertisementData: [String : Any], rssi RSSI: NSNumber) {

        print("didDiscover")

        print("peripheral description:", peripheral.description)

        if let peripheralName = peripheral.name, peripheralName == "Muse-7EF5" {
            muse = peripheral
            muse.delegate = self
            central.stopScan()
            central.connect(muse, options: nil)
        }

    }

    func centralManager(_ central: CBCentralManager, didConnect peripheral: CBPeripheral) {

        print("didConnect")
        print("peripheral:", peripheral)

        peripheral.discoverServices(nil)

    }

}

extension ViewController: CBPeripheralDelegate {

    func peripheral(_ peripheral: CBPeripheral, didDiscoverServices error: Error?) {

        print("didDiscoverServices")

        guard let services = peripheral.services else {
            return
        }

        print("services:")

        for service in services {

            print("	service description:", service.description)

            peripheral.discoverCharacteristics(nil, for: service)

        }

    }

    func peripheral(_ peripheral: CBPeripheral, didDiscoverCharacteristicsFor service: CBService, error: Error?) {

        print("didDiscoverCharacteristicsFor")

        guard let characteristics = service.characteristics else {
            return
        }

        for characteristic in characteristics {

            print("characteristic description:", characteristic.description)

            if characteristic.properties.contains(.broadcast) {
                print("	broadcast")
            }
            if characteristic.properties.contains(.read) {
                print("	read")
            }
            if characteristic.properties.contains(.writeWithoutResponse) {
                print("	write without response")
            }
            if characteristic.properties.contains(.write) {
                print("	write")
            }
            if characteristic.properties.contains(.notify) {
                print("	notify")
            }
            if characteristic.properties.contains(.indicate) {
                print("	indicate")
            }
            if characteristic.properties.contains(.authenticatedSignedWrites) {
                print("	authenticated signed writes")
            }
            if characteristic.properties.contains(.extendedProperties) {
                print("	extended properties")
            }
            if characteristic.properties.contains(.notifyEncryptionRequired) {
                print("	notify encryption required")
            }
            if characteristic.properties.contains(.indicateEncryptionRequired) {
                print("	indicate encryption required")
            }

            if characteristic.properties.contains(.notify) {
                peripheral.setNotifyValue(true, for: characteristic)
            }

            if characteristic.properties.contains(.read) {
                peripheral.readValue(for: characteristic)
            }

        }

    }

    func peripheral(_ peripheral: CBPeripheral, didUpdateValueFor characteristic: CBCharacteristic, error: Error?) {

        print("didUpdateValueFor")

        if let error = error {
            print("error:", error)
        }

        guard characteristic.value != nil else {
            return
        }

        print("characteristic description:", characteristic.description)

    }

    func peripheral(_ peripheral: CBPeripheral, didUpdateNotificationStateFor characteristic: CBCharacteristic, error: Error?) {

        print("didUpdateNotificationStateFor")

        print("characteristic description:", characteristic.description)

    }

}

Here is the output in the debug window:

centralManagerDidUpdateState
central.state is .poweredOn
didDiscover
peripheral description: 
didDiscover
peripheral description: 
didConnect
peripheral: 
didDiscoverServices
services:
    service description: 
didDiscoverCharacteristicsFor
characteristic description: 
    write without response
    notify
characteristic description: 
    notify
characteristic description: 
    notify
characteristic description: 
    notify
characteristic description: 
    notify
characteristic description: 
    notify
characteristic description: 
    notify
characteristic description: 
    notify
characteristic description: 
    notify
characteristic description: 
    notify
characteristic description: 
    notify
characteristic description: 
    notify
characteristic description: 
    notify
characteristic description: 
    notify
characteristic description: 
    notify
characteristic description: 
    notify
characteristic description: 
    notify
didUpdateNotificationStateFor
characteristic description: 
didUpdateNotificationStateFor
characteristic description: 
didUpdateNotificationStateFor
characteristic description: 
didUpdateNotificationStateFor
characteristic description: 
didUpdateNotificationStateFor
characteristic description: 
didUpdateNotificationStateFor
characteristic description: 
didUpdateNotificationStateFor
characteristic description: 
didUpdateNotificationStateFor
characteristic description: 
didUpdateNotificationStateFor
characteristic description: 
didUpdateNotificationStateFor
characteristic description: 
didUpdateNotificationStateFor
characteristic description: 
didUpdateNotificationStateFor
characteristic description: 
didUpdateNotificationStateFor
characteristic description: 
didUpdateNotificationStateFor
characteristic description: 
didUpdateNotificationStateFor
characteristic description: 
didUpdateNotificationStateFor
characteristic description: 
didUpdateNotificationStateFor
characteristic description:

didUpdateValueFor callback function of Core Bluetooth doesn't fire

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