Add a 'How did you hear about us?' dropdown to the WooCommerce block checkout (Additional Checkout Fields API, WC 8.9+)

add-lead-source-dropdown-woocommerce-block-checkout.php

<?php
/**
 * Add a "How did you hear about us?" dropdown to the WooCommerce block checkout.
 *
 * Uses the Additional Checkout Fields API (WooCommerce 8.9+), which only works
 * with the block-based Checkout. Classic shortcode checkouts need the older
 * woocommerce_form_field approach instead.
 *
 * What it does:
 * - Shows an optional select field in the Additional information step of checkout.
 * - Saves the answer to the order automatically (meta key: _wc_other/my-store/lead-source).
 * - Shows the answer on the order confirmation page and on the admin order edit
 *   screen (under the shipping details). No extra display code needed.
 *
 * Storage works on both HPOS and classic post storage. The value is saved through
 * the WC_Order CRUD layer, so WooCommerce writes it to whichever order table the
 * store uses.
 *
 * Notes:
 * - Express checkout flows (Apple Pay, Google Pay, WooPay) skip the checkout form,
 *   so orders placed that way won't have an answer.
 * - The field and its admin display only render while this snippet is active.
 *   Deactivating the snippet hides the field but never deletes saved data.
 * - Change "my-store" to your own namespace and edit the options to fit your store.
 *
 * Tested on WooCommerce 11.0.1 with the block checkout.
 */

defined( 'ABSPATH' ) || exit;

add_action( 'woocommerce_init', function () {
	if ( ! function_exists( 'woocommerce_register_additional_checkout_field' ) ) {
		return;
	}
	woocommerce_register_additional_checkout_field(
		array(
			'id'       => 'my-store/lead-source',
			'label'    => 'How did you hear about us?',
			'location' => 'order',
			'type'     => 'select',
			'required' => false,
			'options'  => array(
				array( 'value' => 'google', 'label' => 'Google' ),
				array( 'value' => 'facebook', 'label' => 'Facebook' ),
				array( 'value' => 'instagram', 'label' => 'Instagram' ),
				array( 'value' => 'podcast', 'label' => 'Podcast' ),
				array( 'value' => 'trade_show', 'label' => 'Trade Show' ),
				array( 'value' => 'newsletter', 'label' => 'Newsletter' ),
				array( 'value' => 'word_of_mouth', 'label' => 'Word-of-mouth' ),
				array( 'value' => 'other', 'label' => 'Other' ),
			),
		)
	);
} );