[Customizing checkout fields using actions and filters] Add custom WooCommerce checkout field to emails

wc-custom-checkout-field-display-in-emails.php.php

/* To use: 
1. Add this snippet to your theme's functions.php file
2. Change the meta key names in the snippet
3. Create a custom field in the order post - e.g. key = "Tracking Code" value = abcdefg
4. When next updating the status, or during any other event which emails the user, they will see this field in their email
*/
add_filter('woocommerce_email_order_meta_keys', 'my_custom_order_meta_keys');

function my_custom_order_meta_keys( $keys ) {
     $keys[] = 'Tracking Code'; // This will look for a custom field called 'Tracking Code' and add it to emails
     return $keys;
}

Hi guys,
can you share the right code to use?

Is not really clear for me.

Thanks.

Hi guys,
can you share the right code to use?

Is not really clear for me.

Thanks.

x2

Full code for adding custom field by product ID, then displaying field value on the order edit page, and then adding to the emails.

* Add fields to the checkout page based on products in cart.
 *
 * @how-to        https://remicorson.com/?p=7871
 * @author        Remi Corson
 * @testedwith    WooCommerce 3.4.0
 */

add_action( 'woocommerce_checkout_fields', 'woo_add_conditional_checkout_fields' );

function woo_add_conditional_checkout_fields( $fields ) {

	foreach( WC()->cart->get_cart() as $cart_item ){
	    $product_id = $cart_item['product_id'];

			if( $product_id == 947 ) {
				$fields['billing']['billing_X'] = array(
					'label'     => __('Billing X, 'woocommerce'),
					'placeholder'   => _x('', 'placeholder', 'woocommerce'),
					'required'  => true,
					'class'     => array('form-row-wide'),
					'clear'     => true
				);
			}

	
	}

	// Return checkout fields.
	return $fields;

} 

/**
 * Display field value on the order edit page
 */
 
add_action( 'woocommerce_admin_order_data_after_shipping_address', 'my_custom_checkout_field_display_admin_order_meta', 10, 1 );

function my_custom_checkout_field_display_admin_order_meta($order){
    echo '<p><strong>'.__('Billing X').':</strong> ' . get_post_meta( $order->get_id(), '_billing_X', true ) . '</p>';
}

/**
 * Add a custom field (in an order) to the emails
 */
add_filter( 'woocommerce_email_order_meta_fields', 'custom_woocommerce_email_order_meta_fields', 10, 3 );

function custom_woocommerce_email_order_meta_fields( $fields, $sent_to_admin, $order ) {
    $fields['billing_X'] = array(
        'label' => __( 'Billling X' ),
        'value' => get_post_meta( $order->id, '_billing_X', true ),
    );
    return $fields;
}