Thêm đoạn code sau vào File funtions.php trong theme:

add_action('woocommerce_after_checkout_billing_form','devvn_xuat_hoa_don_vat');
function devvn_xuat_hoa_don_vat(){
?>
<style>
.devvn_xuat_hoa_don_do {
background: #eee;
padding: 10px;
border-radius: 3px;
}
.devvn_xuat_vat_wrap {
display: none;
}
label.devvn_xuat_vat_input_label {
display: block;
cursor: pointer;
margin-bottom: 0;
}
.devvn_xuat_vat_wrap fieldset {
margin: 10px 0;
padding: 10px;
background: transparent;
border: 1px solid #b0aeae;
}
.devvn_xuat_vat_wrap fieldset legend {
background: transparent;
padding: 0 5px;
margin: 0 0 0 10px;
font-size: 14px;
display: inline;
width: inherit;
border: 0;
text-transform: none;
color: #000;
}
.devvn_xuat_vat_wrap fieldset p {
margin-bottom: 10px;
}
.devvn_xuat_vat_wrap fieldset p:last-child {
margin-bottom: 0;
}
.vat_active .devvn_xuat_vat_wrap {
display: block;
}
</style>
<div class="devvn_xuat_hoa_don_do">
<label class="devvn_xuat_vat_input_label">
<input class="devvn_xuat_vat_input" type="checkbox" name="devvn_xuat_vat_input" value="1">
Xuất hóa đơn VAT
</label>
<div class="devvn_xuat_vat_wrap">
<fieldset>
<legend>Thông tin xuất hóa đơn:</legend>
<p class="form-row form-row-first" id="billing_vat_company_field">
<label for="billing_vat_company" class="">Tên công ty <abbr class="required" title="bắt buộc">*</abbr></label>
<input type="text" class="input-text " name="billing_vat_company" id="billing_vat_company" placeholder="" value="">
</p>
<p class="form-row form-row-last" id="billing_vat_mst_field">
<label for="billing_vat_mst" class="">Mã số thuế <abbr class="required" title="bắt buộc">*</abbr></label>
<input type="text" class="input-text " name="billing_vat_mst" id="billing_vat_mst" placeholder="" value="">
</p>
<p class="form-row form-row-wide " id="billing_vat_companyaddress_field">
<label for="billing_vat_companyaddress" class="">Địa chỉ <abbr class="required" title="bắt buộc">*</abbr></label>
<span class="woocommerce-input-wrapper"><input type="text" class="input-text " name="billing_vat_companyaddress" id="billing_vat_companyaddress" placeholder="" value=""></span>
</p>
</fieldset>
</div>
</div>
<script type="text/javascript">
(function ($) {
$(document).ready(function () {
function check_vat(){
var parentVAT = $('input.devvn_xuat_vat_input').closest('.devvn_xuat_hoa_don_do');
if($('input.devvn_xuat_vat_input').is(":checked")){
parentVAT.addClass('vat_active');
}else{
parentVAT.removeClass('vat_active');
}
}
check_vat();
$('input.devvn_xuat_vat_input').on('change', function () {
check_vat();
});
});
})(jQuery);
</script>
<?php
}
add_action('woocommerce_checkout_process', 'vat_checkout_field_process');
function vat_checkout_field_process()
{
if (isset($_POST['devvn_xuat_vat_input']) && !empty($_POST['devvn_xuat_vat_input'])) {
if (empty($_POST['billing_vat_company'])) {
wc_add_notice(__('Hãy nhập tên công ty') , 'error');
}
if (empty($_POST['billing_vat_mst'])) {
wc_add_notice(__('Hãy nhập mã số thuế') , 'error');
}
if (empty($_POST['billing_vat_companyaddress'])) {
wc_add_notice(__('Hãy nhập địa chỉ công ty') , 'error');
}
}
}
add_action('woocommerce_checkout_update_order_meta', 'vat_checkout_field_update_order_meta');
function vat_checkout_field_update_order_meta($order_id)
{
if (isset($_POST['devvn_xuat_vat_input']) && !empty($_POST['devvn_xuat_vat_input'])) {
update_post_meta($order_id, 'devvn_xuat_vat_input', intval($_POST['devvn_xuat_vat_input']));
if (isset($_POST['billing_vat_company']) && !empty($_POST['billing_vat_company'])) {
update_post_meta($order_id, 'billing_vat_company', sanitize_text_field($_POST['billing_vat_company']));
}
if (isset($_POST['billing_vat_mst']) && !empty($_POST['billing_vat_mst'])) {
update_post_meta($order_id, 'billing_vat_mst', sanitize_text_field($_POST['billing_vat_mst']));
}
if (isset($_POST['billing_vat_companyaddress']) && !empty($_POST['billing_vat_companyaddress'])) {
update_post_meta($order_id, 'billing_vat_companyaddress', sanitize_text_field($_POST['billing_vat_companyaddress']));
}
}
}
add_action( 'woocommerce_admin_order_data_after_shipping_address', 'devvn_after_shipping_address_vat', 99);
function devvn_after_shipping_address_vat($order){
$devvn_xuat_vat_input = get_post_meta($order->get_id(), 'devvn_xuat_vat_input', true);
$billing_vat_company = get_post_meta($order->get_id(), 'billing_vat_company', true);
$billing_vat_mst = get_post_meta($order->get_id(), 'billing_vat_mst', true);
$billing_vat_companyaddress = get_post_meta($order->get_id(), 'billing_vat_companyaddress', true);
?>
<p><strong>Xuất hóa đơn:</strong> <?php echo ($devvn_xuat_vat_input) ? 'Có' : 'Không';?></p>
<?php
if($devvn_xuat_vat_input):
?>
<p>
<strong>Thông tin xuất hóa đơn:</strong><br>
Tên công ty: <?php echo $billing_vat_company;?><br>
Mã số thuế: <?php echo $billing_vat_mst;?><br>
Địa chỉ: <?php echo $billing_vat_companyaddress;?><br>
</p>
<?php
endif;
}