Huh. That's exactly how I have it set up. but there's no redirection. Is it because I'm in test mode on auth.net? I get a white page that says this:

An error occurred while trying to report this transaction to the merchant. An e-mail has been sent to the merchant informing them of the error. The following is the result of the attempt to charge your credit card.

This transaction has been approved.
It is advisable for you to contact the merchant to verify that you will receive the product or service.