WhatsApp for Samsung Galaxy S6 edge+

Edge lighting only triggers for apps you explicitly whitelist, and WhatsApp is off by default. Go to Settings > Edge screen > Edge lighting, turn it on, then tap Manage notifications and enable WhatsApp. If it still doesn't fire, make sure WhatsApp's own notifications are allowed under Settings > Applications > WhatsApp > Notifications, and remember Edge lighting only shows when the screen is off and the phone is face down or lying flat, so a message arriving while you're using the phone won't light the edge. See how others solved this on Reddit

This is almost always a notification-tone or Do Not Disturb issue rather than a phone fault. Open WhatsApp > Settings > Notifications and confirm a Notification tone is set for both Message and Group notifications (not None). Then check Settings > Sounds and vibration > Do not disturb and make sure it isn't active or scheduled. Finally, confirm WhatsApp notifications are allowed under Settings > Applications > WhatsApp > Notifications and that your media/notification volume isn't muted. See how others solved this on Reddit

Samsung's battery optimization puts WhatsApp to sleep in the background, which kills delayed notifications. Go to Settings > Device maintenance > Battery, open the three-dot menu > Settings (or App power management), and add WhatsApp to the list of unmonitored apps so it's never put to sleep. Also make sure background data and unrestricted data aren't blocked for WhatsApp under Settings > Applications > WhatsApp > Mobile data so it can keep its connection alive. See how others solved this on Reddit

Watch notifications mirror the phone, so they only forward when WhatsApp alerts actually fire on the phone first. In the Galaxy Wearable app on the S6 edge+, open Notifications, turn on Notifications, then open Manage notifications (or the app list) and make sure WhatsApp is checked. If nothing comes through, confirm WhatsApp notifications work on the phone itself, since the watch can't show what the phone never received. See how others solved this on Reddit

By default the watch suppresses notifications while you're using the phone, assuming you've already seen them. In the Galaxy Wearable app, go to Notifications and turn off the option that limits alerts when the phone is in use (often labeled show notifications only when the watch is being worn, or block while phone is in use). With that disabled, WhatsApp messages will reach the watch even while the phone screen is on. See how others solved this on Reddit