Web service php file: unable to change "inStock" number with "Product_UpdateInsert"

Question

I am new to php and can't figure out how to change the in stock number through the eCommerce api.
Here is what I am trying:
I'm sure this example looks stupid to all the pros out there.
If someone could just point me in the right direction for resources, that would be helpful.
I suspect "productList" is where it is failing. It gives me no errors but doesn't update the "inStock" quantity to 1900 either.
<?php
$_prod = array("productId" => 2345678 , "productCode" => "YoYo" , "productName" => "4-Piece Accessory Kit" , "inStock" => 1900);
$_pass = array("username" => "username", "password" => "password" , "siteId" => 1234567 , "productList" => $_prod);
$client = new SoapClient("https://domain.worldsecuresystems.com/CatalystWebService/CatalystEcommerceWebservice.asmx? WSDL");
$result = $client->__soapCall('Product_UpdateInsert', array('parameters' => $_pass));
?>

Answer 1

Here is another version I tried and got the same result.
<?php
$_prod = array(
  'productId' => 2345678,
  'supplierCommission' => 0,
  'weight' => 24,
  'inStock' => 1900,
  'inventoryControl' => true,
  'canPreOrder' => false,
  'captureDetails' => false,
  'isOnSale' => false,
  'hideIfNoStock' => false,
  'isGiftVoucher' => false,
  'enableDropShipping' => false,
  'excludeFromSearch' => false,
  'cycletypeCount' => -1,
$_list = array('Products' => $_prod);
$_products = array('ArrayOfProducts' => $_list);
$_pass = array('username' => 'username',
  'password' => 'password',
  'siteId' => 1234567,
  'productList' => $_products);
$client = new SoapClient('https://domain.worldsecuresystems.com/CatalystWebService/CatalystEcommerceWebservice.asmx? WSDL',array('trace' => 1));
$result = $client->__soapCall('Product_UpdateInsert', array('parameters' => $_pass));
print_r(get_object_vars($result));
echo $result;
?>