03-15-2012 09:46 PM - edited 03-15-2012 09:47 PM
Are you just using the Quick Start code or did you set up your own form? If the latter, you would just include additional form fields, either visible or hidden, named according to the API Fields list at the end of the documentation PDF:
http://www.authorize.net/support/DirectPost_guide.pdf
If the former, I suggest reverse-engineering the getCreditCardForm() function in the AuthorizeNetDPM.php file in the lib folder of your SDK. Add fields as necessary from the pdf (see above).
03-15-2012 10:55 PM