Hello, I'm attempting to setup the Purchase event with our Facebook Pixel on our Zen Cart site and I'm having trouble getting it to push the value through.

I've tried a variety of different variables for order total, even the one supplied by Zen Cart on this page, specially "<?php echo $order_summary['order_total']; ?>" and it hasn't worked, regardless of what I try.

The example for the code is below. This would only be on our checkout page to indicate a successful transaction has taken place and it would send the value of the order to the Facebook Ad Manager.

Code:
<script>
  fbq('track', 'Purchase', {
    value: '<?php echo $order_summary['order_total']; ?>',
    currency: 'USD',
  });
</script>
I have tried every variation of the "value" variable possible and none of them seem to successfully pass that order total through to Facebook.

Does anyone know what variable I would enter in for "value" to get that order total to successfully pass through?