Grouping of Notifications not working in Android 8.1 - push-notification

Question

I am using FCM to send notifications on Android Device of 8.1 version.
I am trying to achieve the grouping of notifications , and i have achieved it.
Whenever first notification is in status bar and second notification arrives the first notification disappears. From Second notification on wards all the notifications are shown in the group as expected.
How to solve it ?
Posting Code Snipper below.
if ("FirstTime".equals(new SharedPrefsOperations(this).getPreferencesData("ActiveNotifs"))) {
// I AM EXECUTING THIS ONLY AT FIRST TIME , WHEN THE FIRST NOTIFICATION ARRIVES.
String tempData = new SharedPrefsOperations(this).getPreferencesData("ActiveNotifs");
Notification notification = new NotificationCompat.Builder(this, "MYAPP")
.setSmallIcon(R.mipmap.ic_static_notif)
.setContentTitle(content.getTitle())
.setContentText(tempMsg)
.setAutoCancel(true)
.setContentIntent(pendingIntent)
.setGroup(notifGroup)
.setSound(RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION))
.setChannelId(channel_id)
.setStyle(inboxStyle)
.setGroupSummary(true)
.build();
notificationManager.notify(id, notification);
new SharedPrefsOperations(this).storePreferencesData("ActiveNotifs", "1");
} else {
// I AM EXECUTING THIS FROM SECOND NOTIFICATION ONWARDS
String tempData = new
SharedPrefsOperations(this).getPreferencesData("ActiveNotifs");
Notification notification = new NotificationCompat.Builder(this, "MYAPP")
.setSmallIcon(R.mipmap.ic_static_notif)
.setContentTitle(content.getTitle())
.setContentText(tempMsg)
.setAutoCancel(true)
.setContentIntent(pendingIntent)
.setGroup(notifGroup)
.setSound(RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION))
.setChannelId(channel_id)
.setStyle(inboxStyle)
.build();
notificationManager.notify(id, notification);
new SharedPrefsOperations(this).storePreferencesData("ActiveNotifs", "1");
}

Answer 1

If you are using same id for notifying, it won't work. You need to use a different id for that
Update
Above Android 8.0 (Oreo) Notification Channels are compulsory. So add the notification channel like this. This should be done before notifying.
val mNotificationManager = context.getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
// Android O requires a Notification Channel.
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
val name = context.getString(R.string.app_name)
// Create the channel for the notification
val mChannel = NotificationChannel("channel_id_sms", name, NotificationManager.IMPORTANCE_DEFAULT)
// Set the Notification Channel for the Notification Manager.
mNotificationManager.createNotificationChannel(mChannel)
}