Custom tracking code for the thanks page (only triggers once per order)

wc-custom-tracking-code-for-thanks-page.php

<?php 

add_action( 'woocommerce_thankyou', 'tracking_code', 10, 1 );

function tracking_code( $order_id ) {

    if ( ! $order_id )
        return;

    // Ignore localhost/dev submits
    $localhosts = array(
        '127.0.0.1',
        '::1'
    );

    // Allow code execution only once per order.
    if( !get_post_meta($order_id, '_thankyou_action_done', true) && !in_array($_SERVER['REMOTE_ADDR'], $localhosts) ) {

        // Lets grab the order
        $order = wc_get_order( $order_id );

        // DO ALL YOUR TRACKING STUFF HERE

        // Flag the action as done (to avoid repetitions on reload for example)
        $order->update_meta_data( '_thankyou_action_done', true );
        $order->save();
    }
}

Fix for this issue: https://gist.github.com/woogists/955db81b57a5bf6f7d88fefffef2fa85#gistcomment-3158550