If the application is running in the foreground, iOS won't show a notification banner/alert. That's by design. But we can achieve it by using UILocalNotification as follows

• Check whether application is in active state on receiving a remote
  notification. If in active state fire a UILocalNotification.

  if (application.applicationState == UIApplicationStateActive ) {
  
      UILocalNotification *localNotification = [[UILocalNotification alloc] init];
      localNotification.userInfo = userInfo;
      localNotification.soundName = UILocalNotificationDefaultSoundName;
      localNotification.alertBody = message;
      localNotification.fireDate = [NSDate date];
      [[UIApplication sharedApplication] scheduleLocalNotification:localNotification];
  }
  

SWIFT:

if application.applicationState == .active {
    var localNotification = UILocalNotification()
    localNotification.userInfo = userInfo
    localNotification.soundName = UILocalNotificationDefaultSoundName
    localNotification.alertBody = message
    localNotification.fireDate = Date()
    UIApplication.shared.scheduleLocalNotification(localNotification)
}