Use without composer

[MrMooky]

Currently, I require these files for the webhooks:

require_once 'typo3conf/ext/products/Classes/Coinbase/src/ApiClient.php';
require_once 'typo3conf/ext/products/Classes/Coinbase/src/Util.php';
require_once 'typo3conf/ext/products/Classes/Coinbase/src/Webhook.php';

use CoinbaseCommerce\ApiClient;
use CoinbaseCommerce\Resources\Event;
use CoinbaseCommerce\Webhook;

But right now I end up with the following error:

Class 'CoinbaseCommerce\Resources\Event' not found | Error thrown in file /html/typo3/typo3conf/ext/products/Classes/Coinbase/src/Webhook.php in line 26

Line 26 is this: return new Event($data['event']);

Before this error occurred, I had the error Class 'CoinbaseCommerce\Util' not found, which I "fixed" by including the Util.php file. But I cannot include the file Resources/Event.php, throws an error 500. So I am not sure how to fix this.