After a lot of back and forth with this code, there are a lot of things to troubleshoot to make sure it's playing:

1. Audio Media Playback security issue from Google (since I am using a Chrome-based browser): Autoplay policies.
2. Multiple WebViews: Ensure your WebView is instance-based.
3. Token Usage: Make sure the token is one-time use only. Don’t reuse the same token, or you might have audio issues.
4. Device Permissions: Even if you are setting them correctly in .NET MAUI, ensure you have some fail-safe code.
5. Reset Variables: Make sure you reset variables after every call or failed call.
6. Unmute by Default: Ensure both users are unmuted by default.
7. Subscribe to the Other User Correctly.
8. Don’t Manually Subscribe to Audio: ACS SDK handles this well by itself; meddling with it can cause issues.

FIXES (for each one of the above):

1. Introduce user gesture buttons. Since you are starting and accepting a call, each user should have the corresponding buttons to ensure a user gesture has been given, avoiding autoplay policy issues. Example:

```javascript
startCallButton.addEventListener('click', async () => {
    // Enter code here, such as initiating a call
    call = callAgent.startCall([targetUser], callOptions);
});
```

Or for acceptCallButton:

```javascript
acceptCallButton.addEventListener('click', async () => {
    // Unlock the audio context
    try {
        const audioContext = new (window.AudioContext || window.webkitAudioContext)();
        const source = audioContext.createBufferSource();
        source.buffer = audioContext.createBuffer(1, 1, 22050);
        source.connect(audioContext.destination);
        source.start(0);
        if (audioContext.state === 'suspended') {
            await audioContext.resume();
        }
        console.log('Audio context unlocked.');
    } catch (e) {
        console.error('Error unlocking audio context:', e);
    }

    // Proceed to accept the call
    await acceptCall();
    notifyMAUICallAccepted();
    acceptCallButton.style.display = 'none'; // Hide button after accepting
});
```

2. Single Instance WebView.

To manage multiple WebView instances:

```csharp
if (Instance != null) {
    Console.WriteLine("Attempted to create a second instance of CallPage.");
    return; // Optionally handle as needed
}
Instance = this;
```

Or, if navigating back to the main page:

```csharp
public async void NavigateToMainPage() {
    await MainThread.InvokeOnMainThreadAsync(async () => {
        Application.Current.MainPage = new NavigationPage(new LoginPage());
    });
}
```

3. Token Disposal

Ensure the token is used once by disposing of the CallAgent before reinitializing:

```javascript
if (callAgent) {
    await callAgent.dispose();
    console.log('Existing CallAgent disposed.');
}
```

4. Device Permissions in .NET MAUI

For iOS:

```csharp
if (CallWebView.Handler != null) {
    var iosWebView = (WKWebView)((IWebViewHandler)CallWebView.Handler).PlatformView;
    iosWebView.UIDelegate = new CustomWKUIDelegate();
    iosWebView.Configuration.AllowsInlineMediaPlayback = true;
    iosWebView.Configuration.MediaTypesRequiringUserActionForPlayback = WKAudiovisualMediaTypes.None;
}
```

For Android:

```csharp
if (CallWebView.Handler != null) {
    var androidWebView = (Android.Webkit.WebView)((IWebViewHandler)CallWebView.Handler).PlatformView;
    androidWebView.Settings.JavaScriptEnabled = true;
    androidWebView.Settings.MediaPlaybackRequiresUserGesture = false;
    androidWebView.Settings.DomStorageEnabled = true;
    androidWebView.Settings.DatabaseEnabled = true;
}
```

5. Variable Resetting.

Create a function to reset all call-related variables after each call.

6. Unmute by Default

Ensure users are unmuted when initiating a call:

```javascript
const callOptions = {
    audioOptions: { muted: false },
};

call = callAgent.startCall([targetUser], callOptions);
if (call.isMuted) {
    await call.unmute();
    console.log('Call unmuted after accept.');
}
```

7. Subscribe to Remote Participant

Subscribe to remote participants and handle their video streams:

```javascript
function subscribeToRemoteParticipant(remoteParticipant) {
    console.log(`Remote participant added: ${remoteParticipant.identifier.id}`);

    remoteParticipant.on('isMutedChanged', () => {
        console.log(`Remote participant mute state changed: ${remoteParticipant.isMuted}`);
    });

    remoteParticipant.videoStreams.forEach(remoteVideoStream => {
        subscribeToRemoteVideoStream(remoteVideoStream);
    });

    remoteParticipant.on('stateChanged', () => {
        console.log(`Remote participant state changed to: ${remoteParticipant.state}`);
    });
}
```

Hopefully, this helps! Thank you for your time.