etc/frontend/events.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
    <event name="facebook_businessextension_ssapi_add_to_cart">
        <observer name="facebook_businessextension_ssapi_add_to_cart_after" instance="Facebook\BusinessExtension\Observer\AddToCart"/>
    </event>
    <event name="facebook_businessextension_ssapi_search">
        <observer name="facebook_businessextension_ssapi_search_after" instance="Facebook\BusinessExtension\Observer\Search" />
    </event>
    <event name="facebook_businessextension_ssapi_view_content">
        <observer name="facebook_businessextension_ssapi_view_content_after" instance="Facebook\BusinessExtension\Observer\ViewContent" />
    </event>
    <event name="facebook_businessextension_ssapi_view_category">
        <observer name="facebook_businessextension_ssapi_view_category_after" instance="Facebook\BusinessExtension\Observer\ViewCategory" />
    </event>
    <event name="facebook_businessextension_ssapi_initiate_checkout">
        <observer name="facebook_businessextension_ssapi_initiate_checkout_after" instance="Facebook\BusinessExtension\Observer\InitiateCheckout" />
    </event>
    <event name="facebook_businessextension_ssapi_purchase">
        <observer name="facebook_businessextension_ssapi_purchase_after" instance="Facebook\BusinessExtension\Observer\Purchase" />
    </event>
</config>