# Webhook / Callback

### Overview

Webhooks are powerful tools used to communicate events between different systems over the web. One common application of webhooks is in payment gateways, where they provide real-time notifications about transaction statuses. This page explains how you can use webhooks to know when a payment is completed in your application.

### Setting Up a Webhook for Payment Notifications

#### Configuring the Webhook URL

Whenever you create a transaction you can specify a custom webhook url for the transaction. This helpful if you manage multiple shops.

#### Handling the Webhook Data

When a payment transaction completes, the payment gateway will send a POST request to your configured webhook URL. This request will include important details about the transaction, such as:

* **status**: Indicates the outcome of the transaction (COMPLETED, FAILED).
* **txn**: A unique identifier for the transaction.
* **amount**: The amount that was requested in the transaction.
* **currency**: The currency used for the transaction.
* **customer\_id**: A unique identifier for the customer involved in the transaction.
* **checkout**: The amount that was requested by you but converted to USD.
* **timestamp**: The exact time when the transaction was processed.
* **signature**: md5(txn|timestamp|webhook\_key)

**Example Code Signature PHP:**

```php
<?php

$receivedWebhook = json_decode(file_get_contents('php://input'));

$webhook_key = 'Your_personal_webhook_key';
$timestamp = $receivedWebhook['timestamp'];
$txn = $receivedWebhook['txn'];

$signature = md5($txn . '|' . $timestamp . '|' . $webhook_key); 

if($signature == $receivedWebhook['signature']){
    // Execute your code on success
}

?>
```

You can find your webhook key here:\
<https://malum.co/merchant/settings/api>

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