IOS Firebase push notification issue

ionic ionic-v3
#1

** This code is not working in iOS But properly working in Android .
Getting issue in subscribeToTopic

pushsetup()
{
console.log("*** inside push setup ");
this.fcm.subscribeToTopic(‘all’); //issue is here due to subscribe
this.fcm.getToken().then(token => {
console.log(" token is here ****");
console.log(token);

  //backend.registerToken(token);
  localStorage.setItem('fcmId', token);
    if(this.device.platform){
        this.getDeviceInfo();
    }
});


this.fcm.onNotification().subscribe(response => {
    console.log(response);
  if(response.wasTapped) {
  alert("Received in background");
  } else {
  alert("Received in foreground");
  this.openPopup(response);
  };
},
    msg =>{
        alert("error");
        alert(msg);
    });

// this.fcm.onMessageReceived().subscribe(response => {
// console.log(response)
// });
this.fcm.onTokenRefresh().subscribe(token => {
localStorage.setItem(‘fcmId’, token);
});
}