Step 1: Go to Settings -> Advanced settings -> Battery manager -> Protected apps, then find the app you want to see notifications from (PetBacker app), and protect it. This is "whitelisting" the app so Huawei's overeager software doesn't shut it down for no reason.

Step 2: Go to Settings -> Apps -> advanced -> Ignore battery optimizations, then find the app (PetBacker) and ignore it. Don't be tricked by the misleading wording, "ignoring" the app actually means to let it run, because you're telling the battery optimization function to "ignore" that app.

Step 3: Go to Settings -> Notification panel & status bar -> Notification centre, then find the app (PetBacker), then activate "allow notifications" and also "priority display". You have to activate the priority part too to make sure you get notifications.

Step 4: Go to Settings -> Battery -> App Launch, then find the app (PetBacker), then turn off "Manage automatically" by tapping on the switch to the right of PetBacker .In the pop up menu, enable Auto-launch, Secondary launch, and Run in background options, tap on OK.

Step 5: Restart your phone

Note: If you have Android 8 version of the OS you also need to allow unlimited access to data in the section: Settings -> Apps -> special access -> unlimited data access -> choose PetBacker application and allow it