src/ShopifyApp/resources/database/migrations/2018_08_31_154001_add_plan_to_shops_table_and_charges_table.php
public function up()
    {
        Schema::table('charges', function (Blueprint $table) {
            // Linking
            $table->integer('plan_id')->unsigned()->nullable();
            $table->foreign('plan_id')->references('id')->on('plans');
        });

        Schema::table('shops', function (Blueprint $table) {
            // Linking
            $table->integer('plan_id')->unsigned()->nullable();
            $table->foreign('plan_id')->references('id')->on('plans');
        });
    }
public function up()
    {
        Schema::table('charges', function (Blueprint $table) {
            // Linking
            $table->integer('plan_id')->unsigned()->nullable();
            $table->foreign('plan_id')->references('id')->on('plans');
        });

        Schema::table('shops', function (Blueprint $table) {
            // Linking
            $table->integer('plan_id')->unsigned()->nullable();
            $table->foreign('plan_id')->references('id')->on('plans');
        });
    }
Run the migrations.

@return void