从客户端到服务器获取多个映像所面临的问题，并且foreach循环存在问题

Here I give a view of HTML code, PHP Code and Error after run the code. I also use print_r($_FILES) to check data of array but it show me an empty array.

HTML CODE

<div>
    <label>Upload Multiple Images</label>
    <div>
        <input type="file" id="product_image" name="product_image[]" multiple="true" required="true" />
    </div>
</div>

<div>   
    <button type="submit" name="product_submit" id="product_submit" value="submit">submit</button>
</div>

PHP CODE

<?php

    include("connection.php");

    foreach ($_FILES["product_image"] as $key => $value) 
    {
        $filename = $_FILES["product_image"][$value]["name"];
        echo $filename;
    }

    print_r($_FILES);
<?>

ERROR

Notice: Undefined index: product_image in C:\xampp\htdocs\...
Warning: Invalid argument supplied for foreach() in C:\xampp\htdocs\..
Array ( )