Push notification not working when app is closed (I don't mean in background). I am using cordova-plugin-firebase and @ionic-native/firebase

Notifications are working when app is in foreground and in background but not working when its closed or killed from task tray. Help me here please.

ionic info:

cli packages: (/usr/local/lib/node_modules)

@ionic/cli-utils  : 1.19.2
ionic (Ionic CLI) : 3.20.0

global packages:

cordova (Cordova CLI) : 8.0.0 

local packages:

@ionic/app-scripts : 3.1.9
Cordova Platforms  : android 7.0.0
Ionic Framework    : ionic-angular 3.9.2


Android SDK Tools : 26.1.1
Node              : v8.11.1
npm               : 5.6.0 
OS                : macOS High Sierra