Magento2: frontend event is not working (sales_order_place_after)

In case you do not want to listen to the sales_order_place_after event globally, the correct scope would be webapi_rest instead of frontend.

Thanks for all your support.. this is how I did catch the event..

Company/Vendors/etc/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="sales_order_place_after">
        <observer name="sales_order_grid_vendors_customer" instance="Company\Vendors\Observer\AddVendorOrders" />
    </event>
</config>

Instead of placing your event in Company/Vendors/etc/frontend/events.xml, place it in Company/Vendors/etc/events.xml