view/frontend/layout/checkout_onepage_success.xml (12 lines of code) (raw):
<?xml version="1.0"?>
<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" layout="1column"
xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
<body>
<referenceContainer name="before.body.end">
<block class="Facebook\BusinessExtension\Block\Pixel\Purchase"
name="fbe.pixel.purchase"
template="Facebook_BusinessExtension::pixel/purchase.phtml"
before="-" />
</referenceContainer>
</body>
</page>