I have a Xiaomi phone (MIUI 8)

Step - 1 : Open Security application and select Permissions

step-2 : Select Autostart

Step-3 : Select Skooly Application to enable Autostart

Step-4 : Skooly application will be displayed in Autostart section.

Step-5 : Select Permissions

Step-6 : Select Skooly application.

Step-8 : Scroll down to the last option here which is "Display pop-up Window"

Step-9 : Tap on this option and select "Accept"

Step-10 : Once you see a "Green" check mark for this setting.

Step-11 : Open Mobile Settings and select Battery option.

Step-12 : Tap on Manage apps battery usage

Step-13 : Select Skooly Application

Step-14 : Select No restrictions option.

Step-15 : Once selected No restriction option will be selected.

Step-16: Now Skooly will be displayed under custom section, notifications should work just fine for Skooly app.