Was getting unidentified error so to get identifiable error, downgrade the one signal version by changing One Signal/Editor/OneSignalEditorScript/ Android Support Version + => 27+
After that started getting Dex Limit Error. To remove you need to start building Android Project using Gradle
Follow step given on this link: here
After that when you start building for Gradle you can get an error like Building Error or Gradle Build Failed
Ex. Build-in class shrinker and multidex are not supported yet
from the [android] -> [buildTypes] -> [debug] block.
from the [android] -> [buildTypes] -> [release] block.
To remove issue you need to make sure if build.gradle is correct.
Problem that I faced was:
If you are using Pro Gaurd to minify then make sure to add
If not using minify put false in both place.
try bellow link it gives solution to every problem you will encounter
If started getting error like DaydreamApi Warning then remove minify enables in debug
Use progaurd file and add
If getting error like
Resource '@integer/google_play_services_version' not found in AndroidManifest.xml
<meta-data android:name="com.google.android.gms.version" android:value="@integer/google_play_services_version" />