This Facebook API is Webhooks for Payments that provides real-time updates about your transactions. Webhooks for Payments are an essential method by which you're informed of changes to orders made through Facebook Payments within your app. It is a subscription based system between Facebook and your server that allows your subscribed app to receive updates from Facebook via a specified HTTPS endpoint.
Here are some primary scenarios in which updates are sent to your developer server: Payment Fulfillment, Refunds, Chargebacks, Chargeback Reversals and Declines
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