Trigger event after an order has been created/saved
you can use the event checkout_onepage_controller_success_action
at Namespace\module\etc\frontend\events.xml
:
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
<event name="checkout_onepage_controller_success_action">
<observer name="mymodule_controller_success_action" instance="Namespace\Module\Observer\MyObserver" />
</event>
Observe the sales_order_place_after
event instead.