React Native Firebase ios onNotification doesn't trigger

My project is importing 'react-native-firebase' and I'm trying sending test messages through firebase console using a device token. The method firebase.notifications().onNotification((notification)=>{}) triggers on android devices, but doesn't trigger on ios devices. Notifications don't pop up both on foreground and background. I've tried 'console.log' in the method but doesn't present anything. please let me know what the problem is. I tried 'onMessage()' but it triggers on foreground only.

here's my code:

if (Platform.OS == 'android') {
            this.notificationListener = firebase.notifications().onNotification((notification: Notification) => {
                console.log("onNotification");
                console.log(notification);
                notification
                    .setSound("default")
                    .android.setChannelId('default')
                    .android.setBigText(notification.body, notification.title, '')
                //     .android.setSmallIcon('@mipmap/icon_noti');
                firebase.notifications().displayNotification(notification);
            });
        }
        else {
            this.notificationListener = firebase.notifications().onNotification((notification) => {
                notification.setNotificationId(notification.messageId)
                notification.setSound("default"); 
                notification.setTitle(notification.data.title)
                notification.ios.setBadge(notification.ios.badge ? notification.ios.badge + 1 : 0);
                firebase.notifications().displayNotification(notification);
            });



appDelegate.m: 

#import "AppDelegate.h"

#import <React/RCTBridge.h>
#import <React/RCTBundleURLProvider.h>
#import <React/RCTRootView.h>

#import <GoogleMaps/GoogleMaps.h>
#import <Firebase.h>
#import <FirebaseMessaging.h>
#import "RNFirebaseNotifications.h"
#import "RNFirebaseMessaging.h"
#import "RNSplashScreen.h"

@import Firebase;
@import UserNotifications;

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
  [GMSServices provideAPIKey:@"aasdfsafdadgadgadfasf"];
  RCTBridge *bridge = [[RCTBridge alloc] initWithDelegate:self launchOptions:launchOptions];
  RCTRootView *rootView = [[RCTRootView alloc] initWithBridge:bridge
                                                   moduleName:@"asdb"
                                            initialProperties:nil];

  rootView.backgroundColor = [[UIColor alloc] initWithRed:1.0f green:1.0f blue:1.0f alpha:1]; 
  self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
  UIViewController *rootViewController = [UIViewController new];
  rootViewController.view = rootView;
  self.window.rootViewController = rootViewController;
  [self.window makeKeyAndVisible];
  [FIRApp configure];
  [RNFirebaseNotifications configure];
  [RNSplashScreen show];
  [[UIApplication sharedApplication] registerForRemoteNotifications];
  [[UNUserNotificationCenter currentNotificationCenter] setDelegate:self];
  return YES;
} 

- (void)application:(UIApplication *)application didReceiveRemoteNotification:(nonnull NSDictionary *)userInfo
                                                       fetchCompletionHandler:(nonnull void (^)(UIBackgroundFetchResult))completionHandler{
  [[RNFirebaseNotifications instance] didReceiveRemoteNotification:userInfo fetchCompletionHandler:completionHandler];
}

- (void)application:(UIApplication *)application didRegisterUserNotificationSettings:(UIUserNotificationSettings *)notificationSettings {
  [[RNFirebaseMessaging instance] didRegisterUserNotificationSettings:notificationSettings];
}

- (void)application:(UIApplication *)application didReceiveLocalNotification:(UILocalNotification *)notification {
  [[RNFirebaseNotifications instance] didReceiveLocalNotification:notification];
}

- (NSURL *)sourceURLForBridge:(RCTBridge *)bridge
{
#if DEBUG
  return [[RCTBundleURLProvider sharedSettings] jsBundleURLForBundleRoot:@"index" fallbackResource:nil];
#else
  return [[NSBundle mainBundle] URLForResource:@"main" withExtension:@"jsbundle"];
#endif
}

@end