Authorize.net Integration

[login to view URL] is integrated into two different websites with the same account. Somehow somewhere, something got mixed up and one website is having issues with payments. The client is receiving a decline message, yet they are still processing the payment. They go to pay again and it is successful so they are double charged. The other website works on ARB. Need to make sure that is working correctly. Not looking for sloppy work. Clean up code if necessary and take any unnecessary coding off. Person who did work before started with someone elses template and left unnecessary components making it confusing.