We are in the process of finally getting off AIM API and moving to the new Authorize.Net API. My question is about refunds. If a charge is sent through AIM, then after we switch, can the refund be sent through Authorize.Net API? Is the x_trans_id and transactionKey going to be in sync between the two methods?
Yes, a refund is a refund regardless of which API you are using. As long as you pass in the required information for the refund, as well as meet the other criteria for a valid refund, you can make the initial transaction through the AIM API and make the refund through the new API.