Um, I'm not seeing the "black" settings screen -- which I think is the most important part -- "Notification settings" in Apex Launcher itself.
The blue toggle thing, upper right, has to be enabled (saying "On") -- and the "External notifiers" checkbox has to be enabled (checked) as well.
As for the screenshot with "Your Email app is not supported": I am unable to identify how that error message comes about, but Aqua requires absolutely no configuration on that screen, which is the settings for Apex Notifier.
1 - Apex Notifer just needs to be installed.
2 - Apex Launcher Pro has to have the blue toggle "On" and "External notifiers" checked.