Google Checkout - XML API associate callback serial number with original order

Question

Via the XML API, how do you associate an Google Checkout callback serial number with the original order?

On the same line - What does the serial number in the \"Opt

Answer 1

The way I've done this in the past is using the tag in the original cart, so something like:

 
  
   [some secret about the cart on my system]
  
  
   ...
  
 

Then, after Google has called back with a serial number, I use the Notification History API to retrieve the order details, which then includes my private data, something like:

 
  ...
 
 ...
 ...
 
  ...
  ...
  ...
  ...
  ...
  false
  
   
    [the secret about the cart from my system]
   
   
   
  
  
   ...
  
  
  ...
  
   false
  
  
   ...
  
  ...
  NEW
  REVIEWING
 
 
  
    [the secret about the cart from my system]
  
  
  
 
 
  ...
 
 
 ...
 
  false
 
 
  ...
 
 ...
 NEW
 REVIEWING

I can then use the secret to match the orders up to the details I'd stored in the database previously.