I’ve had lots of questions recently about PayPal IPN (Instant Payment Notification), both from SmartDD and Nickel Script customers. The recurring theme is how can IPN work on several sites?

If you’ve looked at the activation method for IPN, you’ll know that it’s by entering a default IPN URL into your PayPal profile. PayPal’s logic must be that if you want to use IPN, then you must have at least one site with a script that uses it.

I think this then is why the confusion arises, and I too was confused a few years ago when I first used an IPN script and wanted to accept PayPal payments on several sites. I thought that if there was only one IPN URL, then I could only use PayPal with one site.

Seemed logical to me, and I think to most other people too judging by the questions asked.

The truth is, as I mentioned above, it’s just a default URL and not the only one you can use.

When you have two sites that you want to use IPN with, just choose one and use that scripts IPN URL. Then when a payment comes in on the other site, the default IPN URL gets temporarily overridden by that second sites IPN settings.

It works by a setting sent in the POST message sent to PayPal. Inside there is the IPN URL that PayPal is to use for that transaction only. When payment is complete, PayPal sends the transaction data back to the site that initiated the transaction, and not to the default site.

Okay?

So why does SmartDD require that you use the SmartDD IPN URL as the default one? Well the truth is it doesn’t, you can use any IPN URL for any script on any site you have.

The problem has always arisen though that if you’re using an auction site like eBay and selling goods on there (SmartDD v2 and above supports physical goods too), there’s no way to tell SmartDD how to handle the PayPal payment and transaction.

By setting the default IPN URL to point to your SmartDD installation, PayPal will send all the transaction data to SmartDD. As long as you have the title of your eBay listing also identically matched within SmartDD, that will trigger the SmartDD process and automatically send emails to your customer, and record all details of the transaction and your new customer within the SmartDD database.

And with the soon to be released version 3, you can also have CDs or DVDs created and automatically shipped to your customer without you having to do a thing. UPDATE – v3 is now out and supports the sale of physical goods as well as Kunaki.com to have your CDs and DVDs drop shipped to your customers.

-Frank Haywood