Shopping Cart Implementation of PayPal

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As I researched implementation of PayPal as a payment choice, I was happily surprised to find that nearly all the small business oriented shopping cart programs now offer a basic way to allow the customer to remit his payment total using PayPal. Typically, the shopping cart completes its computations of subtotal, shipping, and sales taxes in the shopping cart. Then the customer is allowed to select a payment method. If PayPal is selected, the customer is taken to a secure payment page on PayPal's domain where payment can be made. There the shopper has several choices:

1. Cancel,
2. Process immediately, or
3. Wait or abandon entirely.

Unfortunately, shopping cart systems that haven't implemented PayPal's Instant Payment Notification (IPN), the cart system doesn't have any record of the result. This is the problem that IPN solves by providing extensive feedback about the customer's payment on PayPal.

Shopping Cart Implementation

There are hundreds of shopping cart programs currently in use. Here I list some of the better-known e-commerce applications used by small businesses with their current PayPal implementation status. Most of these offer the first level of PayPal as a payment method; a few offer IPN as well:

What follows is PayPal's list of shopping carts that allow PayPal as a payment method. I have not checked these but provide them for reference. 3D3 ShopFactory, Abarcar, Actinic E-Store for PayPal, Addsoft StoreBot, Advanced Marketing System, Agora Shopping Cart, Americart, Cart32, CF Ezcart, Cartweaver, CatalogIntegrator Cart, CharonCart, ClickCartPro, Comersus Cart, Commission Cart, CoolCart, CyberStrong eShop, Cybertron NetCashier, CyberWiz MysmcStore, Dansie Shopping Cart, drCatalog, DXcart, EarlyImpact ProductCart, eCartsoft, E-Commerce Solutions.Net, Egoods Text-Based Catalog, eMartCart, FPcartPal, HarvesterDX, Hassan Shopping Cart, iCart, iControl WebStudio, IntelliCART, KickASP Shopping Cart, LaGarde StoreFront 5.0, Line9 Tek9 Pro, Mal's e-commerce Shopping Cart, Merchant OrderForm Cart, MetaLinks MetaCart2, Miva Merchant 4, myCart, NetStores E-commerce, OxCart xTRA, PayPalPartner, PerfectStore, PPCal PayPal Calculator, QuickEStore, RealCart, SalesCart, SecureNetShop, ShopCart, Shopping Cart Software, ShoppingQ, SimpleMerce, SmartCart, vShoppingCart, Waverider Systems Perlshop 4.4, WebAssist eCart, WebShopz, X-Cart, US Merchants Associations, VP-ASP Shopping Cart, Zoovy Developer

ShopSite

Since I use ShopSite as one of my own e-commerce applications, I did more extensive testing. ShopSite just added PayPal as a payment type in version 6.2 released in November and December 2002. However, it is only a partial implementation that does not employ PayPal's Instant Payment Notification (IPN) system.

I spoke with a ShopSite engineer who told me that real-time credit card authorization systems on standard payment gateway systems (such as VeriSign PayFlow Pro and Authorize.net) use a different kind of communications interface that stays connected until it receives the transaction's authorization number or "declined" message. PayPal IPN will require entirely different coding to receive the payment notification (PayPal's equivalent of real-time credit card authorization), but will be supported in a later version of ShopSite.

Here's how ShopSite currently implements PayPal. After the shopper fills out the name, address, and e-mail fields, he is taken to PayPal's site for payment. All shopper information is automatically transferred to PayPal where the shopper can complete the transaction, cancel it, or abandon it. The merchant must wait for e-mail confirmation from PayPal that the transaction is complete; there is no automatic notification to the ShopSite software system at present.

However, since ShopSite's e-mail confirmation is sent before the PayPal transaction is confirmed, the shopper receives an e-mail receipt prior to actual payment. This also precludes including in the e-mail confirmation message a URL for immediate digital download. There also seems to be a conflict with some implementations of the order API and redirection to PayPal. (The order API is available with ShopSite Pro only and is used for affiliate program tracking, etc.) My advice to ShopSite storeowners: Unless PayPal is the only payment type you allow, consider delaying PayPal as a payment option until ShopSite updates its program to include PayPal's Instant Payment Notification.

Specialized E-Commerce Applications

Some specialized types of software also incorporate PayPal IPN. These are not full-service shopping carts, but are designed for selling digital goods or tickets. Here is a sampling:

PayLoadz http://www.payloadz.com Provides ASP service based on PayPal IPN for companies wishing to sell digital products. After sale e-mail gives temporary download URL. From $10 per month.

Mollyguard Events http://www.mollyguard.com Provides ASP service based on PayPal IPN for companies selling tickets to events. $1.00 per ticket

Mollyguard Access http://www.mollyguard.com/access Provides ASP service based on PayPal IPN for those selling limited access to website content. 6.5% of access fee

IPN Implementation Scripts

Finally, there are a growing number of scripts in various programming languages that can help developers patch PayPal IPN into their own e-commerce application.

Zykial PayPal IPN Script http://www.zykial.com/paypalipn/paypal.html PHP script e-mails download URL to the customer after transaction is confirmed. $50.00

IPNPAL.com http://www.ipnpal.com ASP implementation that includes an online mailer and a download counter that allows three download attempts. $14.99

Mercsoft PayPal IPN ColdFusion custom tag http://jshop.homeip.net/buy_paypal_ipn.cfm Custom ColdFusion tag receives notification of sale, then writes to database of your choice. Well commented. $15.00

ZephWare PayPal IPN http://zephware.com/?page=shop/software&product_id=58 Provides the code for an IPN add-on to the free, open source phpShop application. http://www.phpshop.org $45

PayPal IPN Interface Tool http://perlsources.com/cgi-bin/catalog/catalog1-a.cgi?report=PayPal:Catalog|Cookies|Cookies|EMail-Bu Provides Perl code and HTML pages to assist developers in creating an IPN interface to PayPal's Shopping Cart and a back-end database (MySQL or PostgreSQL). $10

PayPal IPN File Delivery http://www.jimmelanson.ca/ppipn Sends one or more files attached to an e-mail once a PayPal transaction is confirmed. Written in Perl 5. For Unix or MacOS 5 with sendmail. $49.99 plus $39 for optional installation.

PayPal's IPN Code Samples for logged-in PayPal members. https://www.paypal.com/cgi-bin/webscr?cmd=p/xcl/rec/ipn-code  Provides free IPN code samples for ASP/VBScript, Cold Fusion, Java/JSP, Perl, and PHP.