title: Custom Sound for macosx notification
body: <p>I'm working on project that needs to create a notification in macosx(11.3, Big Sur) with a custom sound.
  I have referenced apple official documents and found an obj-c code that should work which is written below.</p>
  <pre><code>// Configure the notification's payload.
  UNMutableNotificationContent* content = [[UNMutableNotificationContent alloc] init];
  content.title = [NSString localizedUserNotificationStringForKey:@&quot;Hello!&quot; arguments:nil];
  content.body = [NSString localizedUserNotificationStringForKey:@&quot;Hello_message_body&quot;
              arguments:nil];
  content.sound = [UNNotificationSound defaultSound];
   
  // Deliver the notification in five seconds.
  UNTimeIntervalNotificationTrigger* trigger = [UNTimeIntervalNotificationTrigger
              triggerWithTimeInterval:5 repeats:NO];
  UNNotificationRequest* request = [UNNotificationRequest requestWithIdentifier:@&quot;FiveSecond&quot;
              content:content trigger:trigger];
   
  // Schedule the notification.
  UNUserNotificationCenter* center = [UNUserNotificationCenter currentNotificationCenter];
  [center addNotificationRequest:request];
  </code></pre>
  <p>The code works fine, however, when I fix the code to play a custom sound (example.wav) file. It does not apply and still plays the defaultSound.</p>
  <pre><code>...
      UNMutableNotificationContent* content = [[UNMutableNotificationContent alloc] init];
      content.title = [NSString localizedUserNotificationStringForKey:@&quot;Hello!&quot; arguments:nil];
      content.body = [NSString localizedUserNotificationStringForKey:@&quot;Hello_message_body&quot;
                  arguments:nil];
      content.sound = [UNNotificationSound soundNamed:@&quot;example.wav&quot;];
  ...
  </code></pre>
  <p>I have copied the wav file by using Xcode (target &gt; Build Phases &gt; Copy Bundle Resource) which copies the file to the bundles <code>Contents/Resources</code> directory. I believe that the code from the official document should work and I would appreciate any help I can get.</p>