Is it even possible to play sounds for web push notifications?
For Chrome I was able to handle notificationDisplay event and manually play sound. However this event is not supported in Safari.
Nothing mentioned in official documentation at https://documentation.onesignal.com/docs/customize-notification-sounds
In Apple's documentation some Push Package was mentioned. However it's not clear where to put sounds.
It does not seem like web push notifications support sound at the moment. If any sounds do play, they would be due to the settings you might have on, for example, your Mac computer when you receive a notification, or your Android phone if it's set to buzz when you receive a notification.
Sound for web push notifications is in development though. For more information, you can follow these links:
Chrome Thread: https://bugs.chromium.org/p/chromium/issues/detail?id=442131
Firefox Thread: https://bugzilla.mozilla.org/show_bug.cgi?id=1105222
