When processing the payment, Zippy simulates charging money for digital goods. When finished, it redirects to the payment provider (such as WebPay) and sends a post notification. Please see the specification for a diagram of the flow. Exactly what will happen here depends upon the payment processor and the configuration. After these steps have been completed, Zippy will return to the success or error URL. See the How Redirects Work for details.

A real payment processor would probably do things like this:

  • Authentication: set up a user for billing, perhaps with SMS authentication.
  • Direct billing: place a charge on a user’s mobile bill.
  • Credit card billing.

How Redirects Work

When Zippy completes a transaction it redirects to the original success or error URL (see transactions API for how those are defined). In the case of success, the application that began payment would respond with the HTML/CSS/JS needed to dispurse the goods.

A few query string parameters are added to the URL that you can use to reconcile the payment.

This is the original (external) transaction ID that was submitted to the transaction API as ext_transaction_id.
For error redirects only, this string will indicate the type of error. Example: CC_ERROR. Note: it’s up to each payment processor to define their own error codes.

Example: https://site/payments/success/?ext_transaction_id=XYZ


A signed query string notice must be verified before any of the values can be trusted.

How Post Notifications Work

When Zippy completes a transaction it not only redirects to the success/error URL, it also sends a post notification in the background. There are some edge cases in web user agents that could interrupt a redirect request so post notifications are generally more reliable. An application processing a payment should expect to continue the payment flow after redirect but should use post notifications as an additional measure to reconcile payment results.

An application configures its callback URLs when beginning a transaction. Zippy will post a single parameter called signed_notice to either the callback success or error URL. This parameter contains a URL-encoded, signed notice that must be verified and then URL-decoded.

The notice query string has the same parameters as the one sent in a redirect.

Style guide

Zippy contains a full style guide containing the CSS, HTML and JS to be used on a page. It will also contain localisations.

If a page has been implemented in zippy, then it can be used by a payment provider by copying and pasting over the code into the existing payment providers framework. It might be worth payment providers thinking about this step as it creates a bit of a long term maintenance issue.

The style guide is accessible in your zippy checkout, or here:


All the pages are translated. For a status of the translations see:

The translations are available in the zippy repository: