Business events enable external systems to receive notifications from D365 FO apps, enabling business actions to be performed in response. These events occur during a business process, where users perform either workflow or non-workflow actions, such as approval or confirmation of purchases. These events can be used in integration and notification scenarios.
Read more about it using below link
https://d365bits.com/2023/09/02/how-to-send-notifications-to-teams-using-business-events-d365-fo/
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