I am using Huawei P9 / P9 Lite (EMUI 4)

 Step 1: Goto "Settings" and tap on "Apps" 

Step 2: Click on "Advanced"

Step 3: Tap on "Configure Apps"

Step 4: Tap on "Ignore Optimisations" 

Step 5:. Tap on "Scroll" button next to the "Allowed" apps section from the top.

Step 6:. Select "All apps" such that you can see "Skooly" on the list

Step 7: Tap on "Skooly" and select "Allow"

  

Step 8:. Once allowed, you should receive push notifications properly from Skooly app.