madeincosmos

add_filter( 'woocommerce_email_customer_details_fields', 'add_user_id_to_woocommerce_emails', 10, 3);

function add_user_id_to_woocommerce_emails( $fields, $sent_to_admin, $order ) {
  $user_id = $order->get_customer_id();
  $user_info = get_userdata( $user_id );
  
  $fields['user_id'] = array( 
    'label' => __( 'User ID', 'woocommerce' ),  
    'value' => $user_id
  );