Hi Joshua,
Did you get this working for you? I am using the osCommerce 2.2rc2a with Authorize.net. I tried Jeff Wigal's error messaging code after the $transaction_response, but I got nothing. I have talked to my host people and they said the cURL was right because they have others using osCommerce and it is working for them. I have tried calling Authorize.net support, but they will not help me without an error number. I have checked the API Login, transaction key, and MD5 Hash. I did read that the MD5 Hash code should be 16 characters long, mine is not. I have read through everyones issues on this topic. I feel like I have tried them all myself. What do you think I should try at this point?
Help! - Pera