[ic] Paypal IPN?
cwenham at synesmedia.com
Tue Dec 23 13:23:15 EST 2003
On Tuesday 23 December 2003 04:04, Tom wrote:
> Im trying to develop a PayPal IPN Gateway with interchange My question is
> when User selects PayPal as a payment option where do I put the code to
> require the PayPal Gateway? Anyone can help me develop this will be great.
IPN needs a URL for PayPal to POST a form to, so you'll need to create either
a standalone CGI program for PayPal to POST to, or create a page in the
catalog's "pages" directory that contains the code to do your magic.
BUT... IPN integration has been looked at for Interchange several times in
the past, but there's a big problem that implementors keep running into. If I
have this right, I think it goes like this:
1) There is no way to avoid sending the customer off to PayPal's web site,
because you can't take the customer's PayPal username and password and then
masquarade as that user to PayPal. (Despite being against PayPal terms of
service, It's not even worth trying, because you have no way of knowing what
source of funds attached to the customer's PayPal account they want to use.)
2) PayPal does not automatically redirect the customer back to your site once
the payment is complete. The best you can get is a little "Continue" button
on the final page of the PayPal sequence, which you can program to take the
customer back to your site. Not every customer will remember to click on that
button, so it's not a reliable way to inform Interchange that the payment was
3) IPN should theoretically solve that problem, because PayPal will POST a
form to any URL you specify when the payment is complete. But this POST will
come from PayPal's IP address and not the customer's, so Interchange will not
recognize it as part of the same session. That means any Interchange page
called by that POST will be in a new session with an empty shopping basket
and no customer information.
The only way to get around the IP address mismatch is to run Interchange in
WIDEOPEN mode, which opens up a security hole and isn't really an option in a
serious production environment.
4) Last but not least, even if you do somehow get Interchange to use the
contents of the IPN POST within the customer's session, there still isn't a
reliable way to get the customer's browser back to your site so you can show
her the receipt page. I think the best you can do is to display a message
asking the customer to click on the "Continue" button at the end of the
PayPal sequence before you send her to PayPal's site, and then hope the
customer remembers it.
This is the reason why most Interchange users and consultants I know of still
recommend just adding a link or a pop-up window on the Receipt page. You can
record the order, deliver the receipt to the customer, and then explain very
clearly that the customer still has to go through PayPal before their order
Chris Wenham - Synesmedia, Inc.
516-620-4110 / 1-888-255-7573
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