$token = ''; // Set your API token
$client = new Koren\ErplyBooks\Client($token);

$response = $client->Invoices()->get(); // Koren\ErplyBooks\Response\ItemsResponse

$response = $client->Invoices()->get(1); // Koren\ErplyBooks\Response\ItemResponse

$invoices = $client->Invoices()->get(); // Koren\ErplyBooks\Response\ItemsResponse

// Items response is iterable
foreach ($invoices as $invoice) {
    // Do something with $invoice
}

// Responses are jsonable
$json = json_decode($response); // json string of all items or item

// Responses are countable
$count = count($response); // integer (how many items were in response)