Cannot get Apple Media Service Bluetooth BLE to work With Various Bluetooth Boards or Arduino

Hello. Having a hard time with this one.

The Apple Media Service is documented here (1). It seems like an elegant and simply system to control audio over BLE with a custom hardware solution.

I have set up various boards I have, including Arduino Nano BLE and Adafruit Huzzah ESP32, using fairly straightforward scripts.

This "device" I am building then should show up on the iPhone > Settings App > Bluetooth > Other Devices. I should able to connect to the device, and have it get media information from the iPhone and be able to control it

What happens is a bit odd. First nothing shows up in Other Devices. I then use a BLE integrator app like BLE Scanner, and it shows up as Arduino (despite what I name it). I can connect to it, and interesting it lists APPLE MEDIA as a service UUID (which is correct!).

Now if I go back to Settings App > Bluetooth, because I have connected to my device with BLE Scanner, it shows as connected and under "My Devices" ! However it doesn't work, no audio is controlled. As a test I tried flicking the Play Pause characteristic but it does nothing (can see it in the Arduino code below where it flips every 4 second).

Is there an example of using Apple Media Device BLE control? I found one using MicroPython but I don't want to use micropython, and I am not sure what I am doing different.

The Arduino code is here. I have been trying to get this to work for a while now, using many, many different boards / chips. Any help is appreciated:

BLEService mediaService("89D3502B-0F36-433A-8EF4-C502AD55F8DC");

BLEUnsignedCharCharacteristic audioControlChar("9B3C81D8-57B1-4A8A-B8DF-0E56F7CA51C2", BLEWrite | BLENotify); 

BLEUnsignedCharCharacteristic entityUpdateChar("2F7CABCE-808D-411F-9A0C-BB92BA96C102", BLEWrite | BLENotify); 
BLEUnsignedCharCharacteristic entityAttributeChar("C6B2F38C-23AB-46D8-A6AB-A3A870BBD5D7", BLEWrite | BLERead); 

int playPauseSwitch = 1;  // for now flip between 0 (pause) and play (1) on 9B3C81D8 characteristic, every 4 seconds
long previousMillis = 0;  // count for test to flip play pause

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

  pinMode(LED_BUILTIN, OUTPUT); 

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

    while (1);
  }

  BLE.setLocalName("MediaController");

  mediaService.addCharacteristic(audioControlChar); 
  mediaService.addCharacteristic(entityUpdateChar);
  mediaService.addCharacteristic(entityAttributeChar);
  
  BLE.setAdvertisedService(mediaService); // add the service UUID
  BLE.addService(mediaService); 

  BLE.advertise();

  Serial.println("Bluetooth device active, waiting for connections...");
}

void loop() {
  // wait for a BLE central
  BLEDevice central = BLE.central();

  // if a central is connected to the peripheral:
  if (central) {
    Serial.print("Connected to central: ");
    // print the central's BT address:
    Serial.println(central.address());
    // turn on the LED to indicate the connection:
    digitalWrite(LED_BUILTIN, HIGH);

    while (central.connected()) {
      long currentMillis = millis();
      // For now flip play pause characteristics every 4 seconds
      if (currentMillis - previousMillis >= 4000) {
        previousMillis = currentMillis;
        flipPlayPause();
      }
    }
    // when the central disconnects, turn off the LED:
    digitalWrite(LED_BUILTIN, LOW);
    Serial.print("Disconnected from central: ");
    Serial.println(central.address());
  }
}

void flipPlayPause() {

  if (playPauseSwitch == 0) {
    playPauseSwitch = 1;
  } else {
    playPauseSwitch = 0;
  }

  audioControlChar.writeValue(playPauseSwitch);

}

(1) - Apple BLE Media Service https://developer.apple.com/library/archive/documentation/CoreBluetooth/Reference/AppleMediaService_Reference/Introduction/Introduction.html#//apple_ref/doc/uid/TP40014716-CH2-SW1