Android System Overlay Window Not Working

I am building and Android app and trying to learn all I can in the process. As a test I wanted to add a 'chat heads' style overlay to the system. So, I looked around and found some

Solution 1:

for apps targeting Android 8.0

apps must use a new window type called TYPE_APPLICATION_OVERLAY.

so for Android 8.0 you must ask this permission, for lower verison

SYSTEM_ALERT_WINDOW permission

will work

For more Refer this link

https://developer.android.com/about/versions/oreo/android-8.0-changes.html#cwt