I’m new to PHP and WooCommerce customization, and I’ve attempted to implement a custom checkout field for collecting a Tax Exempt Number. While I have managed to create and display the field, I’m not sure if my implementation is complete. I’d appreciate any input or guidance on my setup and I apologize if I haven’t posted this correctly.

I’ve reviewed the following during my research:

• BusinessBloomer: WooCommerce: How to Add a Custom Checkout Field
• WooCommerce Customize Checkout Fields
• Stack Overflow: Load user custom data on WooCommerce admin new order custom fields
• Stack Overflow: Get and display the inputed data from custom Checkout fields in WooCommerce

What I tried:

1. I used the woocommerce_billing_fields filter to add a new field for the Tax Exempt Number to the billing section of the checkout.
2. I utilized the woocommerce_checkout_create_order action to save the field data to both the order meta and the user meta.
3. Display in Admin Order Details:

• Included the field using the woocommerce_admin_billing_fields filter.
• I ensured that the field data is loaded via AJAX (woocommerce_ajax_get_customer_details) when selecting a customer for a manual order.

4. Allowed admin to correct field value using the woocommerce_process_shop_order_meta action.
5. I utilized the woocommerce_order_details_after_customer_details action to show the field in customer order details and thank you page (when logged in). And woocommerce_email_customer_details to display the field in email notifications.

Here’s the complete code I have implemented so far:

/**
 * WooCommerce: Custom Billing Checkout Field (Tax Exempt #)
 */
function custom_checkout_fields_settings() {
    $text_domain = 'woocommerce';
    return array(
        'tax_exempt_number' => __('Tax Exempt #', $text_domain),
    );
}

// Add Tax Exempt # Field to Checkout and My Account Edit Address
add_filter( 'woocommerce_billing_fields' , 'custom_billing_field' );
function custom_billing_field( $fields ) {
    $fields['billing_tax_exempt_number'] = array(
        'label'     => __('Tax Exempt #', 'woocommerce'),
        'placeholder'   => _x('Enter Your Tax Exempt Number', 'placeholder', 'woocommerce'),
        'required'  => true,
        'class'     => array('form-row-wide'),
        'clear'     => true,
        'priority'    => 35,
    );
    return $fields;
}

// Display Tax Exempt # Field on admin edit order page
add_filter( 'woocommerce_admin_billing_fields', 'admin_single_order_custom_addresses_fields' );
function admin_single_order_custom_addresses_fields( $fields ) {
    $settings = custom_checkout_fields_settings();

    foreach ( $settings as $field_key => $field_label ) {
        $fields[$field_key] = array(
            'label'         => $field_label,
            'show'          => '0',
            'wrapper_class' => 'form-field-wide',
        );
    }
    return $fields;
}

// Load Ajax Tax Exempt # Field data as customer billing address field
add_filter( 'woocommerce_ajax_get_customer_details', 'add_custom_fields_to_ajax_customer_details', 10, 3 );
function add_custom_fields_to_ajax_customer_details( $data, $customer, $user_id ) {
    // $settings = custom_checkout_fields_settings();

    // foreach( $settings as $field_key => $field_label ) {
    //     $data['billing'][$field_key] = $customer->get_meta('billing_'.$field_key);
    // }

    // error_log(print_r($data,true));

    $data['billing']['tax_exempt_number'] = $customer->get_meta('billing_tax_exempt_number');

    return $data;
}


// Add Tax Exempt # Field to WooCommerce billing address in user profile
add_filter( 'woocommerce_customer_meta_fields' , 'user_profile_custom_fields' );
function user_profile_custom_fields( $fields ) {
    $fields['billing']['fields']['billing_tax_exempt_number'] = array(
        'label' => __( 'Tax Exempt #', 'woocommerce' ),
        'description' => '',
    );
    return $fields;
}

// Display Tax Exempt # Field on email notifications
add_action('woocommerce_email_customer_details','display_custom_fields_on_emails_notifications', 30, 4 );
function display_custom_fields_on_emails_notifications( $order, $sent_to_admin, $plain_text, $email ) {
    $settings = custom_checkout_fields_settings(); // Load settings

    // Loop through setting fields
    foreach ( $settings as $field_key => $field_label ) {
        $meta_value = $order->get_meta('_billing_'.$field_key);
        if ( ! empty($meta_value) ) {
            echo '<div><strong>' . $field_label . ':' . '</strong> <span class="text">' . $meta_value . '</span></div>';
        }
    }
}

// Save the Tax Exempt # Field from the admin order edit screen and update the user meta
// Note: Allow admin to correct any errors
add_action( 'woocommerce_process_shop_order_meta', 'save_custom_billing_field_and_update_user_meta', 45, 2 );

function save_custom_billing_field_and_update_user_meta( $order_id, $post ) {
    $order = wc_get_order( $order_id );

    $settings = custom_checkout_fields_settings(); // Load Settings

    foreach ( $settings as $field_key => $field_label ) {
        if ( isset( $_POST['_billing_' . $field_key] ) ) {
            // Save the order meta data
            $order->update_meta_data('_billing_' . $field_key, sanitize_text_field( $_POST['_billing_' . $field_key] ));
            
            // Also update the user meta data if a customer ID is present
            if ( $order->get_customer_id() ) {
                update_user_meta( $order->get_customer_id(), 'billing_' . $field_key, sanitize_text_field( $_POST['_billing_' . $field_key] ) );
            }
        }
    }

    $order->save_meta_data();
}


// Save the Tax Exempt # Field (once order is placed)
add_action( 'woocommerce_checkout_create_order', 'save_custom_billing_field_on_create_order', 20, 2 );
function save_custom_billing_field_on_create_order( $order, $data ) {
    if ( isset( $_POST['billing_tax_exempt_number'] ) && ! empty( $_POST['billing_tax_exempt_number'] ) ) {
        $order->update_meta_data('_billing_tax_exempt_number', sanitize_text_field( $_POST['billing_tax_exempt_number'] ) );
        update_user_meta( $order->get_customer_id(), 'billing_tax_exempt_number', sanitize_text_field( $_POST['billing_tax_exempt_number'] ) );
    }
}

// Display Tax Exempt # Field in order details customer section using user meta
// Note: Shows on Thank You Page if User is Logged in.
add_action( 'woocommerce_order_details_after_customer_details', 'display_tax_exempt_number_in_order_details' );
function display_tax_exempt_number_in_order_details( $order ) {
    // Get the user ID from the order
    $user_id = $order->get_user_id();

    // Get the tax exempt number from the user meta
    $tax_exempt_number = get_user_meta( $user_id, 'billing_tax_exempt_number', true );

    // If it exists, display the tax exempt #
    if ( ! empty( $tax_exempt_number ) ) {
        echo '<p style="font-style:italic;"><strong>' . __('Tax Exempt #:', 'woocommerce') . '</strong> ' . esc_html( $tax_exempt_number ) . '</p>';
    }
}