If there’s no sound on incoming messages, please check if the notifications are activated in the mysms settings (Sidebar – Notifications – Ringtone – Activate Ringtone). In case you think that everything is correctly set, you can also try to reset the ringtone and to restart mysms afterwards.
My notifications don’t work at all (Android 5.x)
With Android 5.x Google implemented some new options for the notifications.
General: Android Lollipop offers several options for general and sound notifications. We would recommend to set the “Priority” mode for mysms. This ensures that you always get notified on incoming messages. You can do this directly in the Android settings on your phone (Sound & Notification – App Notification – mysms – Priority).
Popup: The mysms popup is not available anymore, as it has been replaced by the heads-up notification, which comes directly from the Android system. To customize this notification, go to the Android Settings - Sound and Notification – Interruptions. Here you can select/deselect priority interruptions. You’ll find further useful information concerning the notification settings in Android Lollipop here.