Open Messenger tap the 3 dots and go into Settings > Notifications > enable Show Notifications and Allow Sound and Vibration. Make sure you enable Show app icon badges, also in the same window go down to Notification Categories > enable new messages . Now go back to main settings > More Settings > Text and Multimedia Messages and in both of those make sure Show when delivered are enabled. Enabling all of these are necessary bc your phone will likely vibrate or make sound for all kinds of apps and services, so it is a visual verification of messages.
