1.) Include the autoloader
require_once('/path/to/client/autoload.php');
2.) Instantiate the "PaymentGateway\Client\Client" with your credentials, send the transaction and react on the result.
master
$client = new Client("username", "password", "apiKey", "sharedSecret");
$customer = new Customer();
$customer->setBillingCountry("AT")
->setEmail("customer@email.test");
$debit->setTransactionId("uniqueTransactionReference")
->setSuccessUrl($redirectUrl)
->setCancelUrl($redirectUrl)
->setCallbackUrl($callbackUrl)
->setAmount(10.00)
->setCurrency('EUR')
->setCustomer($customer);
$result = $client->debit($debit);
if ($result->isSuccess()) {
//act depending on $result->getReturnType()
}