Issue: no sound notification on my Android devices (phone and tablet).
Found that even if all notification are enabled (related to sound), no audio or default sound was assigned for the app.
Device: Android phones, running android 10 and MIUI ver.12
Fix: Using Settings app on Android: Settings -> Apps -> Manage Apps then selecting the Synology chat app. Select Notifications and under Notification Categories selected Chat, then assigned a ringtone for the sound.
Device: Android Tablet running Android 10
Fix: Using Settings App: Settings -> Apps & Notifications, selecting the Synology chat app. Selecting Notifications -> Chat -> Advanced, select preferred sound.
Article from: https://itkb.nazarene.org/itkb/article.php?id=271
