XF 2.1 Add custom tracking code

[Saido]

Hello, how can I add this custom tracking code from this page https://sesionweb.com

This is the tracking code

<!-- Pixel Code for https://sesionweb.com/ -->
<script async src="https://sesionweb.com/pixel/6DmYyzNSW"></script>
<!-- END Pixel Code -->

I tried to put it on PAGE_CONTAINER template but its not working, please help me.