# Notifications

Notifications (a.k.a "Callbacks", "IPN") are used in 0xpay to alert users about events happenning to their merchants. Whenever something happens to your merchant, 0xpay will try to send a webhook to the **Notifications URL** that you've previously specified in [merchant settings](https://docs.0xpay.app/integration-cookbook/getting-started/merchant-setup#notifications). 

{% hint style="warning" %}
Webhooks require [authorization](https://docs.0xpay.app/public-api/broken-reference) on your side, in order to verify the validity of message received.
{% endhint %}

{% hint style="success" %}
We guarantee that webhooks will come in described order, according to their tx status change.

*For example:* we won't send you a "Done" status webhook until you respond with success HTTP status to a "Pending" webhook that was sent earlier.
{% endhint %}

### **Notifications retry timeline:**

{% hint style="info" %}
In case your URL responds with a *non-success HTTP status* – the notification will be retried **10 times,** with initial delay of **10 minutes,** each new retry triggered **15 minutes** later, up to a maximum of **60 minutes.** In total, we are going to try and notify you for **8 hours.**
{% endhint %}

| Number of Retries | Timeout |
| ----------------- | ------- |
| Retry #1          | 10 min  |
| Retry #2          | 25 min  |
| Retry #3          | 40 min  |
| Retry #4          | 55 min  |
| Retry #5-10       | 60 min  |

Check out notification examples on the next page.