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How to Prevent Duplicate Order Charges in WP E-Commerce

Updated on November 7, 2014

Preventing Duplicate Charges

Duplicate orders can happen for a number of reason in WP E-Commerce, usually the result of a bug or server error. This doesn’t tend to be a problem unless of course your customers are being charged more than once for the same order. At its core, WP E-Commerce does not verify if a user’s cart has been paid for before sending it through a merchant gateway. Herein lies the problem. To prevent a user from being charged more than once for a single order, WordPress needs to keep track of which user carts have been paid for and prevent carts from being processed through a merchant gateway if it’s already been processed. Sound tricky? Well we made a plugin that does this!
The WPEC Prevent Duplicate Charges plugin is available for download on GitHub (


About the WPEC Plugin

This plugin is for WP E-Commerce carts experiencing occasional duplicate charges. The cause can be the result of PHP errors, your bad code, or user error. But the root problem, I found, is the same. This plugin doesn’t fix the problems in your code, but it will prevent your customers from being charged more than once for a single order, even if caused by server issues or user error.

How the WPEC Plugin Works

If for any reason an order has been submitted for checkout more than once, it will not be allowed to proceed through the designated gateway, and instead redirected to transaction results. The plugin will go through the following:

  1. When an order is submitted at checkout, we check to see if the current cart has been associated with an approved purchase log
  2. If it has, then we redirect to transaction results immediately, empty the cart, and don’t let the merchant do anything
  3. If it hasn’t, then we add hooks to narrow in at the moment a merchant updates the transaction to “Approved”
  4. At this moment, we update wpecdup_processed_cart_[uniqueid] to contain the session of the purchase_log, so we know it’s been paid for

When the WPEC Plugin Fails

The WPEC Prevent Duplicate Charges plugin relies on a universal merchant plugin. The merchant plugin relays the information between the consumer’s credit card, the issuer and back to the merchant plugin. The merchant plugin regulates the communication between the cart and the bank. The bank controls whether the information is either approved or denied.
When a merchant plugin’s submit() function is called, if an error is thrown before the merchant plugin has had a chance to call set_transaction_details, then this plugin will not work. If this plugin does not prevent duplicate orders for you, then an error lies in the submit() function of the merchant plugin.

The Growth of E-Commerce

More than 40 percent of online users have used a desktop computer, tablet or mobile device to buy a product. A predicted 47.8 percent of digital users will use e-commerce in 2018. Mobile devices make the internet easily available and business profiles are imperative to keep up with the competition. Now with the birth of apps, businesses can sell thousands, if not millions, of dollars in products. If you are a developer, it is time to jump on the bandwagon and know the right tools to building a great e-commerce site. A properly running cart is one of the most important factors of a website. The WPEC Prevent Duplicate Charges plugin can help keep your website development business afloat!


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