Uncaught Error: Class 'net\authorize\api\contract\v1\MerchantAuthenticationType'

[gmrstudios]

Hello and thanks for reading. I am fairly fluent with the use of APIs and PHP in general but keep running into issues with utilizing the authorize.net API. My long term goal is to give our clients the ability to enter their payment information into Authorize.net with the goal of being able to charge them for recurrent billing. I loaded SDK through composer. Everything looks like it loaded as intended but when calling the various classes it is getting errors. 

<?php
require '../vendor/autoload.php'; 
use net\authorize\api\contract\v1 as AnetAPI;
use net\authorize\api\controller as AnetController;

define("AUTHORIZENET_LOG_FILE","phplog");

// Common setup for API credentials  
  $merchantAuthentication = new AnetAPI\MerchantAuthenticationType();   
  $merchantAuthentication->setName("********");   
  $merchantAuthentication->setTransactionKey("********");   
  $refId = 'ref' . time();

// Create the payment data for a credit card
  $creditCard = new AnetAPI\CreditCardType();
  $creditCard->setCardNumber("4111111111111111");  
  $creditCard->setExpirationDate( "2038-12");
  $paymentOne = new AnetAPI\PaymentType();
  $paymentOne->setCreditCard($creditCard);

// Create a transaction
  $transactionRequestType = new AnetAPI\TransactionRequestType();
  $transactionRequestType->setTransactionType("authCaptureTransaction");   
  $transactionRequestType->setAmount(151.51);
  $transactionRequestType->setPayment($paymentOne);
  $request = new AnetAPI\CreateTransactionRequest();
  $request->setMerchantAuthentication($merchantAuthentication);
  $request->setRefId( $refId);
  $request->setTransactionRequest($transactionRequestType);
  $controller = new AnetController\CreateTransactionController($request);
  $response = $controller->executeWithApiResponse(\net\authorize\api\constants\ANetEnvironment::SANDBOX);   

if ($response != null) 
{
  $tresponse = $response->getTransactionResponse();
  if (($tresponse != null) && ($tresponse->getResponseCode()=="1"))
  {
    echo "Charge Credit Card AUTH CODE : " . $tresponse->getAuthCode() . "\n";
    echo "Charge Credit Card TRANS ID  : " . $tresponse->getTransId() . "\n";
  }
  else
  {
    echo "Charge Credit Card ERROR :  Invalid response\n";
  }
}  
else
{
  echo  "Charge Credit Card Null response returned";
}
?>

This seems fairly straight-forward but I must be missing something. Thanks for reading.