更新您的表单以包含新的未输入字段：

<label for="proof_images">Proof of Expense (Image):</label>
<input type="file" id="proof_images" name="proof_images[]" accept="image/*" multiple>

修改JavaScript代码以处理文件上传沿着其他表单数据。您需要使用FormData对象通过AJAX请求将文件发送到服务器。

jQuery(document).ready(function($) {
    $('#expense_form').on('submit', function(e) {
        e.preventDefault();
        var orderid = $('#exp_order_no').val();
        var expense = $('#expense_amt').val();
        var expense_reason = $('#expense_reason').val();
        var formData = new FormData(this);

        $.ajax({
            url: '<?php echo admin_url('admin-ajax.php'); ?>',
            type: 'POST',
            data: {
                action: 'update_custom_field_order_expense_php',
                orderid: orderid,
                expense: expense,
                expense_reason: expense_reason,
            },
            processData: false, // Prevent jQuery from processing the data
            contentType: false, // Prevent jQuery from setting content type
            data: formData, // Use the FormData object
            success: function(response) {
                // Handle success
                console.log('Custom field updated successfully.');
                alert('Expense Submitted Successfully !!');
                location.reload();
            },
            error: function(response) {
                // Handle error
                console.log('Failed to Submit Expense.');
                alert('Failed to Submit Expense. Contact Online Team.');
                location.reload();
            }
        });
    });
});

然后更新update_custom_field_order_expense_php函数来处理文件上传并将其保存到所需的目录：

function update_custom_field_order_expense_php() {
    // ... Your existing code ...

    // Handle file uploads
    if (!empty($_FILES['proof_images']['name'])) {
        $upload_dir = wp_upload_dir();
        $target_dir = $upload_dir['basedir'] . '/2023/Expense_images/';

        // Create the target directory if it doesn't exist
        if (!file_exists($target_dir)) {
            wp_mkdir_p($target_dir);
        }

        $file_count = count($_FILES['proof_images']['name']);

        for ($i = 0; $i < $file_count; $i++) {
            $file_name = $_FILES['proof_images']['name'][$i];
            $file_tmp_name = $_FILES['proof_images']['tmp_name'][$i];

            // Generate a unique file name to prevent overwriting
            $unique_filename = wp_unique_filename($target_dir, $file_name);

            $target_file = $target_dir . $unique_filename;

            // Move the uploaded file to the target directory
            if (move_uploaded_file($file_tmp_name, $target_file)) {
                // You can store the file paths or URLs in your order's metadata
                // Example: $order->update_meta_data('Expense Proof Image ' . ($i + 1), $target_file);
            }
        }
    }

    // ... Your existing code ...
}

这段代码将处理多个文件上传，并将它们存储在/wp-content/uploads/2023/Uploads_images/目录中，并使用唯一的文件名。然后，您可以选择如何将这些文件路径或URL与订单元数据中的相应订单ID相关联，如代码中的注解所示。
这是一个基本的例子。但是，在实现文件上传时，重要的是要优先考虑安全性，以防止各种形式的攻击和漏洞。因此，请确保检查文件类型，大小等内容：

$allowed_mime_types = array('image/jpeg', 'image/png', 'image/gif');
if (!in_array($_FILES['proof_images']['type'][$i], $allowed_mime_types)) {
    // Handle invalid file type
}

$max_file_size = 5 * 1024 * 1024; // 5 MB
if ($_FILES['proof_images']['size'][$i] > $max_file_size) {
    // Handle oversized file
}

更新：

我试着调试代码和修复和可能的问题，但我无法通过代码片段插件激活PHP代码，因为它给我错误状态400.我给整个代码波纹管，请让我知道我如何才能解决这个问题。

<form id="expense_form" class="expense_form" action="" method="post" enctype="multipart/form-data">
   <label for="order-id">Order ID:</label>
   <input class="exp_order_no" id="exp_order_no" type="text" pattern="[0-9]*" placeholder="Enter the Order Number" required>

   <label for="expense">Expense:</label>
   <input class="expense_amt" id="expense_amt" type="text" pattern="[0-9]*" placeholder="Enter the expense amount" required>

   <label for="reason">Reason for Expense:</label>
   <textarea class="expense_reason" id="expense_reason" name="reason" rows="4" placeholder="Enter Message" required></textarea>

   <label for="my_image_upload">Upload Image:</label>
   <input type="file" name="my_image_upload[]" id="my_image_upload" accept="image/*" required multiple>

   <input type="submit" class="exp_but" id="exp_but" value="Submit">
</form>

<script>
jQuery(document).ready(function($) {
   $('#expense_form').on('submit', function(e) {
       e.preventDefault();
       var orderid = $('#exp_order_no').val();
       var expense = $('#expense_amt').val();
       var expense_reason = $('#expense_reason').val();
       var formData = new FormData(this);

       // Debugging: Output form data to console
       console.log('Order ID:', orderid);
       console.log('Expense:', expense);
       console.log('Expense Reason:', expense_reason);
       console.log('Form Data:', formData);

       $.ajax({
           url: '<?php echo admin_url('admin-ajax.php'); ?>',
           type: 'POST',
           data: formData, // Use formData to send all form data
           processData: false,
           contentType: false,
           enctype: 'multipart/form-data', // Specify enctype for file uploads
           success: function(response) {
               // Handle success
               console.log('Custom field updated successfully.');
               alert('Expense Submitted Successfully !!');
               location.reload();
           },
           error: function(response) {
               // Handle error
               console.log('Failed to Submit Expense.');
               alert('Failed to Submit Expense. Contact Online Team.');
               location.reload();
           }
       });
   });
});
</script>

add_action('wp_ajax_update_custom_field_order_expense_php', 'update_custom_field_order_expense_php');
add_action('wp_ajax_nopriv_update_custom_field_order_expense_php', 'update_custom_field_order_expense_php');

function update_custom_field_order_expense_php() {
   $order_id = sanitize_text_field($_POST['orderid']);
   $order_expense = sanitize_text_field($_POST['expense']);
   $order_expense_reason = sanitize_text_field($_POST['expense_reason']);
   $order = wc_get_order($order_id);

   if (!empty($_FILES['my_image_upload']['name'])) {
       $upload_dir = wp_upload_dir();
       $target_dir = $upload_dir['basedir'] . '/2023/Expense_images/';

       if (!file_exists($target_dir)) {
           wp_mkdir_p($target_dir);
       }

       $file_count = count($_FILES['my_image_upload']['name']);

       for ($i = 0; $i < $file_count; $i++) {
           $file_name = $_FILES['my_image_upload']['name'][$i];
           $file_tmp_name = $_FILES['my_image_upload']['tmp_name'][$i];

           $unique_filename = wp_unique_filename($target_dir, $file_name);

           $target_file = $target_dir . $unique_filename;

           if (move_uploaded_file($file_tmp_name, $target_file)) {
               $order->update_meta_data('Expense Proof Image ' . ($i + 1), $target_file);
           }
       }
   }

   $order->update_meta_data('Driver Expense', $order_expense);
   $order->update_meta_data('Driver Expense Reason', $order_expense_reason);
   $order->save();

   // Debugging: Send a JSON response
   wp_send_json_success('Expense submitted successfully.');
}