So, I followed the instructions on 15 Minute Quick Start Guide and was able to successfully post to my Authorize.net sandbox account. However, whenever I try to handle Authorize.net's response using:
SIMResponse authNetResponse = new SIMResponse(form);
bool valid = authNetResponse.Validate(authNetMd5, apiLoginId);
valid always returns false.
At first I was passing an empty string for authNetMd5 since it was not set in the Merchant profile. But then I created a new MD5, and set it in the merchant profile and passed it into the Validate function using the authNetMd5 variable. Still no luck.
Despite the fact that it always returns false, the rest of the values in the SIMResponse look okay.
The only thing is that the authNetResponse.MD5Hash property does not match the x_fp_hash value that is generated by the DPMFormGenerator.OpenForm helper, or the MD5 value I set in the merchant profile.