Нужно channel задавать для Notification
if(android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.O) {
var importance = NotificationManager.IMPORTANCE_HIGH
var notificationChannel = NotificationChannel("$id" ,NOTIFICATION_CHANNEL_NAME + "$id", importance)
notificationChannel.enableLights(true)
notificationChannel.lightColor = Color.RED
notificationChannel.enableVibration(true)
notificationChannel.vibrationPattern = longArrayOf(100, 200, 300, 400, 500, 400, 300, 200, 400)
mBuilder.setChannelId("$id")
mNotificationManager.createNotificationChannel(notificationChannel)
}