FCM using push notification ionic 4 - ionic-framework

Question

FCM using push notification ionic 4
i had attach my error log too,
i installed https://ionicframework.com/docs/native/fcm
i am using ionic cli---4.12.0
I am trying to send push notification on my device with the help of FCM
and ionic 4. But I'm unable to get token,. I'm getting device token for iOS
and I've import app.module.ts,app.component.ts aslo ,
i have try to store token in local storage but im getting null value
is there i missing??
initializeApp() {
this.platform.ready().then(() => {
this.statusBar.styleLightContent();
this.splashScreen.hide();
this.fcm.subscribeToTopic('marketing');
//Receving
this.fcm.getToken().then((token) => {
localStorage.setItem('token', token);
}, (err) => {
alert(JSON.stringify(err));
});
this.fcm.onNotification().subscribe((data) => {
console.log("Data :", data);
if (data.wasTapped) {
console.log("Received in background " + JSON.stringify(data));
alert("Received in background " + JSON.stringify(data));
} else {
console.log("Received in foreground" + JSON.stringify(data));
alert("Received in foreground" + JSON.stringify(data));
}
});
//Updating
this.fcm.onTokenRefresh().subscribe((token) => {
localStorage.setItem('token', token);
console.log(token);
alert('refresh token: ' + token);
});
this.fcm.unsubscribeFromTopic('marketing');
});
}