Bitpay\InvoiceInterface::getOrderId PHP Method

    public function getOrderId();

 /**
  * @inheritdoc
  */
 public function createInvoice(InvoiceInterface $invoice)
 {
     $request = $this->createNewRequest();
     $request->setMethod(Request::METHOD_POST);
     $request->setPath('invoices');
     $currency = $invoice->getCurrency();
     $item = $invoice->getItem();
     $buyer = $invoice->getBuyer();
     $buyerAddress = $buyer->getAddress();
     $this->checkPriceAndCurrency($item->getPrice(), $currency->getCode());
     $body = array('price' => $item->getPrice(), 'currency' => $currency->getCode(), 'posData' => $invoice->getPosData(), 'notificationURL' => $invoice->getNotificationUrl(), 'transactionSpeed' => $invoice->getTransactionSpeed(), 'fullNotifications' => $invoice->isFullNotifications(), 'notificationEmail' => $invoice->getNotificationEmail(), 'redirectURL' => $invoice->getRedirectUrl(), 'orderID' => $invoice->getOrderId(), 'itemDesc' => $item->getDescription(), 'itemCode' => $item->getCode(), 'physical' => $item->isPhysical(), 'buyerName' => trim(sprintf('%s %s', $buyer->getFirstName(), $buyer->getLastName())), 'buyerAddress1' => isset($buyerAddress[0]) ? $buyerAddress[0] : '', 'buyerAddress2' => isset($buyerAddress[1]) ? $buyerAddress[1] : '', 'buyerCity' => $buyer->getCity(), 'buyerState' => $buyer->getState(), 'buyerZip' => $buyer->getZip(), 'buyerCountry' => $buyer->getCountry(), 'buyerEmail' => $buyer->getEmail(), 'buyerPhone' => $buyer->getPhone(), 'guid' => Util::guid(), 'token' => $this->token->getToken());
     $request->setBody(json_encode($body));
     $this->addIdentityHeader($request);
     $this->addSignatureHeader($request);
     $this->request = $request;
     $this->response = $this->sendRequest($request);
     $body = json_decode($this->response->getBody(), true);
     $error_message = false;
     $error_message = !empty($body['error']) ? $body['error'] : $error_message;
     $error_message = !empty($body['errors']) ? $body['errors'] : $error_message;
     $error_message = is_array($error_message) ? implode("\n", $error_message) : $error_message;
     if (false !== $error_message) {
         throw new \Exception($error_message);
     }
     $data = $body['data'];
     $invoiceToken = new \Bitpay\Token();
     $invoice->setToken($invoiceToken->setToken($data['token']))->setId($data['id'])->setUrl($data['url'])->setStatus($data['status'])->setBtcPrice($data['btcPrice'])->setPrice($data['price'])->setInvoiceTime($data['invoiceTime'] / 1000)->setExpirationTime($data['expirationTime'] / 1000)->setCurrentTime($data['currentTime'] / 1000)->setBtcPaid($data['btcPaid'])->setRate($data['rate'])->setExceptionStatus($data['exceptionStatus']);
     return $invoice;
 }