CRM api updating records

CRM api updating records

Brief background of what I'm trying to achieve:

Someone fills in an enquiry form on our website about a specific product.
I use the crm api (with php) to insert the enquirer's details as a lead into the crm and get the lead id from the response and save it as $enquiryid.
I then insert the product details with a duplicate check into the products module in the crm and get the product id from the response and save it as $propertyid.

I now want to update the lead to add the product to the lead. (Easily done manually via the web interface)

I have tried the following
  1. $xml = '<Products>';
  2.  $xml .= '<row no="1">';
  3.  $xml .= '<FL val="PRODUCTID">'.$propertyid.'</FL>';
  4.  $xml .= '</row>';
  5.  $xml .= '</Products>';

  6. header("Content-type: application/xml");
  7.  $url = "https://crm.zoho.eu/crm/private/xml/Leads/updateRecords";
  8.  $param= "authtoken=".$token."&scope=crmapi&newFormat=1&id=".$enquiryid."&xmlData=".$xml;
  9.  $ch = curl_init();
  10.  curl_setopt($ch, CURLOPT_URL, $url);
  11.  curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1);
  12.  curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
  13.  curl_setopt($ch, CURLOPT_TIMEOUT, 30);
  14.  curl_setopt($ch, CURLOPT_POST, 1);
  15.  curl_setopt($ch, CURLOPT_POSTFIELDS, $param);
  16.  $result = curl_exec($ch);
  17.  curl_close($ch);
  18. echo $result;
I am getting a response back that record has been updated successfully but when I look in crm at both leads and products neither has been associated i.e. in the lead record there is no related product and in the product record there is no related lead???
Have I got my logic wrong somewhere? And if response is saying record has been updated, what has actually been updated??