Debugging Credit Card Processing

We had working fine using the AuthorizeNet.Aim processor setting. I changed the method from Authorize & Capture to Authorize only and it stopped working. So I changed it back to Authorize & Capture, still not working. I verified all the credentials are correct. I verified there is no transactions coming through on the side. As if it isn’t even connecting.

How can I see exactly what is going on, on the CS-Cart side so I can identify the cause of the problem?

We are getting the card is declined but we are using cards we know are good and isn’t seeing the decline. It is as if the CS-Cart error message is ambiguous and/or misleading.