$config   = new Xi\Netvisor\Config(...);       // Use the parameters described above.
$netvisor = new Xi\Netvisor\Netvisor($config);

$customers = $netvisor->getCustomers(
    '1234567-1' // Optional keyword
);

$customers = $netvisor->getCustomersChangedSince(
    new DateTime(...) // Required
);

$product = $netvisor->getProduct(
    123 // Required Netvisor identifier
);

$customer = new Xi\Netvisor\Resource\Xml\Customer(
    new Xi\Netvisor\Resource\Xml\CustomerBaseInformation(
        '1234567-1',
        'Test Oy',
        'Test street 1',
        'Helsinki',
        '00240',
        'FI'
    )
);

$response = new \SimpleXMLElement($this->netvisor->sendCustomer($customer));
$netvisorIdentifier = (string)$response->Replies->InsertedDataIdentifier;

$invoice = new Xi\Netvisor\Resource\Xml\SalesInvoice(...);

$invoiceProductLine = new Xi\Netvisor\Resource\Xml\SalesInvoiceProductLine(...);

$invoice->addSalesInvoiceProductLine($invoiceProductLine);

$netvisor->sendInvoice($invoice);