Integration Guide

Third-Party Shopping Carts – The Cart Upload Command
Implementing the Instant Update API With the Cart Upload Command
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330 June 2012 PayPal Payments Standard Integration Guide
 Follow PayPal-defined semantics and syntax – Adhere to well-formed variable names
and syntax rules in the callback response to PayPal. If errors occur in the response, PayPal
uses the fallback options.
 Ensure a consistent and good buyer experience – When fallback shipping options are
used, you should honor the rates to ensure a consistent and good buyer experience.
 Localize shipping options – Return localized shipping options, based on the buyer’s
country and locale, which PayPal sends in the callback request.
Other Considerations for Implementing Instant Update
When you implement the callback, you must consider callback response errors, .timeouts, and
shipping options.
Callback Response Errors
If there are any callback response errors, PayPal responds by displaying the fallback options
on the PayPal Review Your Payment page. To obtain the richer set of options available
through the callback, exercise care in the syntax and values you specify and test the callback
integration.
Minimum and Maximum Shipping Options
You can specify up to 10 shipping options for the fallback options in the HTML code for the
Cart Upload command and for the detailed options based on shipping address in the callback
response. You must specify at least 1 shipping option.
Callback Timeouts
If the callback does not return within the timeout period, PayPal displays the fallback shipping
options you specified in the HTML code for the Cart Upload command in the drop-down
menu on the PayPal Review Your Payment page.
The PayPal Review your information page in the figure below shows 2 shipping options
from which the buyer can choose if the callback times out. An amount of $1.00 is offered for
insurance: