> ## Documentation Index
> Fetch the complete documentation index at: https://docs.billions.works/llms.txt
> Use this file to discover all available pages before exploring further.

# PHP SDK

> Install and use the official Billions PHP SDK.

The PHP SDK requires PHP 8.1 or newer and uses Guzzle 7.8 or newer.

<Card title="PHP SDK on GitHub" icon="github" href="https://github.com/billions-works/billions-sdk-php" cta="View repository">
  Browse the source code, examples, releases, and issue tracker.
</Card>

## Installation

```bash theme={null}
composer require billions-works/sdk-php
```

## Initialize the client

```php theme={null}
<?php

require 'vendor/autoload.php';

use Billions\BillionsApi;

$api = new BillionsApi($_ENV['BILLIONS_API_KEY']);
```

You can also provide a custom host, API version, or Guzzle client:

```php theme={null}
$api = new BillionsApi(
    apiKey: $_ENV['BILLIONS_API_KEY'],
    baseUrl: 'https://api.billions.works',
    version: 'v1',
    httpClient: $customGuzzleClient,
);
```

## Available methods

```php theme={null}
$api->getVersion();
$api->getCurrencies();
$api->getMerchantInfo();
$api->estimateFees($payload);
$api->createInvoice($payload);
$api->getInvoice($invoiceId);
$api->getInvoicesByOrderNo($orderNo);
$api->verifyInvoicePaid($invoiceId, $callbackData);
$api->verifyInvoicePaid($callbackDataWithId);
```

API objects are returned as associative arrays with field names matching the
public API JSON.

## Errors

| Exception                       | Meaning                                                         |
| ------------------------------- | --------------------------------------------------------------- |
| `BillionsApiException`          | The API request failed; exposes `statusCode` and `responseBody` |
| `InvoiceNotPaidException`       | The retrieved invoice is not completed                          |
| `CallbackVerificationException` | Callback data differs from the API invoice                      |

See [Handle a callback](/examples/handle-a-callback) for verification code.