GST ID Address Fields

				
add_filter( 'woocommerce_default_address_fields', 'wpturbo_add_custom_default_address_field' );

/**
 * Add custom default address field to WooCommerce checkout form.
 *
 * @param array $fields The existing WooCommerce default address fields.
 *
 * @return array The modified default address fields.
 */
function wpturbo_add_custom_default_address_field( array $fields ): array {
	$fields['wpturbo-has-business-gst-id'] = [
		'label' => 'Are You a Registered Business With a GST ID?',
		'class' => ['wpturbo-has-business-gst-id'],
		'type' => 'checkbox',
	];
	return $fields;
}

add_filter('woocommerce_customer_meta_fields', 'wpturbo_add_address_field_to_admin_profile_page');

/**
 * Add custom address field to WooCommerce admin user profile.
 *
 * @param array $admin_fields The existing WooCommerce customer meta fields.
 *
 * @return array The modified customer meta fields.
 */
function wpturbo_add_address_field_to_admin_profile_page( array $admin_fields ): array {

	$admin_fields['billing']['fields']['billing_wpturbo-has-business-gst-id'] = [
		'label' => 'Are You a Registered Business With a GST ID?',
		'description' => '',
	];
	return $admin_fields;

}