I'm using Authorize.Net's Direct Post Method (DPM) to process credit card transactions. I am not able to process credits (x_type = 'CREDIT') through DMP and Auhtorize.Net support loosely told me it's not possible and that I must use the AIM method or the Virtual Terminal for processing refunds. I don't want to use the AIM method because it puts our business within scope of PCI requirements and I don't want to use the virtual terminal because it adds a lengthy step in the selling workflow. Has anyone solved this problem, or even encountered this problem?
Using AIM for credits does not cause PCI issues because you're not handling the credit card information. All you need to do is send back the transaction ID and last four digits of the card number through AIM and the credit will be issued. See page 14 of the AIM guide for how credits are done.