first upload all files

Modules/FlashSale/Resources/lang/en/attributes.php

@@ -0,0 +1,15 @@
+<?php
+
+return [
+    'product' => 'Product',
+    'end_date' => 'End Date',
+    'price' => 'Price',
+    'quantity' => 'Quantity',
+    'campaign_name' => 'Campaign Name',
+
+    // validation
+    'products.*.product_id' => 'Product',
+    'products.*.end_date' => 'End Date',
+    'products.*.price' => 'Price',
+    'products.*.qty' => 'Quantity',
+];