I am using Lenovo phone (Android 5.0)

Step 1: Open your device 'Security' settings

Step 2: Now tap on "Speed"

Step 3: Now tap on "AutoStart Management"

Step 4: Select Skooly from this list and turn ON the slider such that it turns to Blue.

Step 5: Now go back to the "Autostart Management" screen and tap on "Protected List"

Step 6: Tap on "Add" and select Skooly, notifications should work just fine for Skooly app.