Openpay LIBRARY

Hi, I'm new in CI, I'm using version 4.0 and I'm dealing with the same problem, I don't know how to integrate Openpay library in order to use it as a payment gateway.
Here's where Openpay repo is for PHP: https://github.com/open-pay/openpay-php

I created a folder under app/Libraries/Openpay
Inside has the Openpay.php file, data and resources folders

In my cart controller in app/Controllers I added the following line:

use App\Libraries\Openpay;

Adding this line where I need it under the controller:
Openpay::setId('moiep6umtcnanql3jrxp');
I got the error that "Openpay" was not found.

I also tried following the above example and still no luck.
I also I added with composer : composer require openpay/sdk
But I don't know how to include the autoloader

Any guide/help/advice is more than welcome, thanks in advance.