NiLS uses a technique called "overlay window" to be able to display notifications on top of all other apps, including the stock lock screen.
Android 8.0 (Oreo), as a security measure, had prevented all apps from drawing on top of the stock lock screen, to prevent an abuse of this feature to block a user from accessing its phone.
Unfortunately this means, that NiLS can no longer display its notifications on top of the Android 8.0 stock lock screen.
However, there is a possible workaround:
- Install a 3rd party lock screen such as WidgetLocker, C-Locker, ZUI Lock Screen or any other lock screen that works on Android Nougat.
- Enable it (without notifications) to replace your stock lock screen.
- Go to NiLS > Lock Screen and enable "Auto detect lock screen" option.
- Make sure that NiLS has "app usage access" permission.
- Turn off the screen, wait few seconds so the lock screen will become active, than turn it on again.
- You'll see a popup "Lock screen has been detected", click "Yes" to get NiLS notifications on top of it.
- You might need to enable "auto hide service" from the main NiLS service, if it doesn't work smoothly.
Please note that on some lock screen apps you'll need to disable stock security such as pin code or pattern unlock.
Anyway, I'm working on a new version of NiLS that will have its own lock screen so you won't need a 3rd party lock screen app and it will work with the stock security (pin code, pattern or fingerprint unlock) but it will take some time until it will be ready.