Facebook states the following: If you have multiple values that you want to track, you can also dynamically update this value by using a server-side variable (ex: you can insert your shopping cart value into the value field of the pixel that uses the checkout pixel).
I am using the following code to track purchases on my order confirmation page:
<!-- Facebook Pixel Code -->
<script>
!function(f,b,e,v,n,t,s){if(f.fbq)return;n=f.fbq=function(){n.callMethod?
n.callMethod.apply(n,arguments):n.queue.push(arguments)};if(!f._fbq)f._fbq=n;
n.push=n;n.loaded=!0;n.version='2.0';n.queue=[];t=b.createElement(e);t.async=!0;
t.src=v;s=b.getElementsByTagName(e)[0];s.parentNode.insertBefore(t,s)}(window,
document,'script','//connect.facebook.net/en_US/fbevents.js');
fbq('init', '314191338731885');
fbq('track', "PageView");
fbq('track', 'Purchase', {value: '0.00', currency: 'USD'});
</script>
<noscript><img height="1" width="1" style="display:none"
src="https://www.facebook.com/tr?id=314191338731885&ev=PageView&noscript=1"
/></noscript>
<!-- End Facebook Pixel Code -->
What does it mean when they say
By using a server-side variable (ex: you can insert your shopping cart value into the value field of the pixel that uses the checkout pixel).
It means use your server side code (PHP, .NET, Java, etc) to modify the HTML/JS sent to the client to include the purchase value you want logged in the
I.e instead of just outputting
fbq('track', 'Purchase', {value: '0.00', currency: 'USD'});
Set the value based on some information your server side code has access to (for example, the actual purchase value of the order which was jus tplaced)