yehudah

<?php

/**
 * Get field key for field name.
 * Will return first matched acf field key for a give field name.
 * 
 * ACF somehow requires a field key, where a sane developer would prefer a human readable field name.
 * http://www.advancedcustomfields.com/resources/update_field/#field_key-vs%20field_name
 * 
 * This function will return the field_key of a certain field.

yehudah

/**
 * Add the field to order emails
 **/
add_filter('woocommerce_email_order_meta_keys', 'my_custom_checkout_field_order_meta_keys');
function my_custom_checkout_field_order_meta_keys( $keys ) {
    $keys[‘My Field 1′] = ‘_my_field_1;
    $keys[‘My Field 2′] = ‘_my_field_2′;
    return $keys;
}