We setup using the Direct Post Method with SIM page back in September 2015.

We log the response code received from Auth.Net.

We've noticed that we get a few of these Reponse Code 3 with Reason Code 98: Duplicate Fingerprint messages that using the time and database saving of the order can link to a Payment that has a transaction id in the Auth.Net transaction logs.

Because of this response the user usually ends up attempting to do the transaction again and thus gets two transactions instead of one.

We think we have narrowed this down to users using the browser's Back Button and we are looking at how we can prevent that from occuring.

We are trying to understand why an Error Response Code is still processing a payment?  At what point is this error occuring?  If this is happening on the SIM page is there a way to get the response with the successful processing prior to getting the error?