# Overview Webhooks are user-defined **HTTP callbacks** triggered by an **event**. 8Pay uses webhooks to asynchronously let your application know when events happen, like payments are completed, customers subscribe to plans, subscriptions are cancelled, billings are executed and so on. When an event occurs, 8Pay makes an HTTP POST request to the URL you have configured for your webhook, sending a notification of the event. Your application can then perform whatever logic is necessary. ## Verify integrity Each notification is identified by a unique id generated hashing the rest of the notification with the sha256 algorithm. To verify its integrity you can compare the id with the sha256 hash of the notification itself, stripped of its id. ## Retry logic 8Pay attempts to deliver the notifications for up to three days with an exponential back off. If your webhook has been removed when we attempt a retry, future retries of that event will be prevented. However, if you change a webhook endpoint before we’re able to retry, you should still expect to see future retry attempts. ## Verify events are sent from 8Pay To confirm that received events are sent from 8Pay, you can use the **Webhook Notifications API** to retrieve the notifications by their id. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.8pay.network/webhook-notifications/overview.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.