can insert both so and soitem into db, but have an error

database/migrations/2018_05_15_034032_create_soitems_table.php

@@ -15,7 +15,6 @@ class CreateSoitemsTable extends Migration
     {
         Schema::create('soitems', function (Blueprint $table) {
             $table->increments('id');
-
             // foreign key for the so table
             $table->unsignedInteger('so_id');
             $table->foreign('so_id')

database/seeds/DatabaseSeeder.php

@@ -11,6 +11,7 @@ class DatabaseSeeder extends Seeder
      */
     public function run()
     {
-        // $this->call(UsersTableSeeder::class);
+         //$this->call(UsersTableSeeder::class);
+         $this->call(SoSeeder::class);
     }
 }

database/seeds/SoSeeder.php

@@ -0,0 +1,29 @@
+<?php
+
+use Illuminate\Database\Seeder;
+use App\So;
+use Carbon\Carbon;
+
+class SoSeeder extends Seeder
+{
+    /**
+     * Run the database seeds.
+     *
+     * @return void
+     */
+    public function run()
+    {
+         DB::table('sos')->insert([
+          
+        // 'id' => '8',
+        'ff_id' => '4', 
+        'supplier_company_name' => 'SEED',
+        'supplier_contact_person' => 'SEED',
+        'supplier_contact_person_no' => '1234',
+        'delivery_id' => '4',
+        'warehouse_id' => '4',
+        'created_at' => Carbon::now()->format('Y-m-d H:i:s'),
+        'updated_at' => Carbon::now()->format('Y-m-d H:i:s'),
+       ]);
+    }
+}

database/seeds/SoitemSeeder.php

@@ -0,0 +1,64 @@
+<?php
+
+use Illuminate\Database\Seeder;
+use App\Soitems;
+use Carbon\Carbon;
+
+class SoitemSeeder extends Seeder
+{
+    /**
+     * Run the database seeds.
+     *
+     * @return void
+     */
+    public function run()
+    {
+       
+         DB::table('soitems')->insert([
+             
+        ([
+          
+        // 'id' => '8',
+        'so_id' => '2', 
+        'status' => '0',
+        'order_id' => '1',
+        'brand_no' => '1',
+        'model_no' => '1',
+        'item_code' => '1', 
+        'quantity_of_item' => '1',
+        'uom' => 'SEED',
+        'quantity_of_carton' => '1',
+        'packaging_type' => '1',
+        'packaging_height' => '1',
+        'packaging_width' => '1',
+        'packaging_depth' => '1',
+        'packaging_gross' => '1',
+        'packaging_nett' => '41',
+        'created_at' => Carbon::now()->format('Y-m-d H:i:s'),
+        'updated_at' => Carbon::now()->format('Y-m-d H:i:s'),
+
+         ]),
+        ([
+         // 'id' => '8',
+        'so_id' => '2', 
+        'status' => '0',
+        'order_id' => '1',
+        'brand_no' => '1',
+        'model_no' => '1',
+        'item_code' => '1', 
+        'quantity_of_item' => '1',
+        'uom' => 'SEED',
+        'quantity_of_carton' => '1',
+        'packaging_type' => '1',
+        'packaging_height' => '1',
+        'packaging_width' => '1',
+        'packaging_depth' => '1',
+        'packaging_gross' => '1',
+        'packaging_nett' => '41',
+        'created_at' => Carbon::now()->format('Y-m-d H:i:s'),
+        'updated_at' => Carbon::now()->format('Y-m-d H:i:s'),
+        ]),
+        
+       ]);
+    }
+}