What does the in-app message sound mean?
In-App Message Sound sets the volume controls when receiving new messages while the app is open or running in the background. The In-App Message Sound can be controlled in the app Settings. The default app volume setting is Follow system, which means that sound will correspond with the user’s device volume settings.
Choosing Always high volume will ensure that you receive the Alert tone even if your device volume is down or set to mute. Again, this setting only applies if the app is open or running in the background.
Choosing the In-App Alert Sound None means that you will not receive the Alert tone when an Alert is sent while the app is open or running in the background.