How to group FCM notifications in flutter

How to group FCM notifications (having in one stack if there is more than one notification), I tried using the 'tag' key in my payload (as It was suggested in other answers) but it makes that new notification replaces the last notification.

This what I am using for notification:

data: {
            'notification': {
                'title': notificationTitle,
                'body': notificationBody,
            },
            'priority': 'high',
            'data': {
                'click_action': 'FLUTTER_NOTIFICATION_CLICK',
                'id': '1',
                'status': 'done'
            },
            'to': userToken
           },
}