Which Authorize.net API to use?

I recently answered a question on the Authorize.net forum. The questioner wanted to know which API to use for a single, one-time transaction. Below is my answer. You may find it helpful in determining which Authorize.net API to use for your purposes.

• Use AIM to make a single payment in real-time while the customer is using your application/website and has their credit card in-hand, and (if your application is a website) your site has an SSL certificate installed such that all senstive credit card information is entered via a from over an https:// connection.
• Use SIM if the above is true but you do not have an SSL certificate installed (and do not plan to install one).
• Use CIM if you want to support storing the customer’s credit card (or bank account, if you support it) information so the customer does not have to re-enter it if they return to your site *or* you have a recurring billing situation where either the amount or frequency of billing fluctuates.In either case, you will need the SSL certificate / https:// connection for when the customer enters their payment information.

The other common factor which causes people to choose AIM over SIM is they want to maintain the branding of their site when the customer pays. When you use SIM, the customer is sent to a form hosted by Authorize.net to enter their payment information. You can customize the header and footer somewhat, and change the background color and a couple other things, but you cannot do anything like add links back to your site or add your normal menus, etc.

This is just a quick summary of the key differences between and uses for the different Authorize.net APIs. I plan to write an Authorize.net 101 post one of these days, which provides a high-level overview of their primary payment gateway APIs.  In the meantime, if you need more information, you should refer to Authorize.net’s own documentation, or check out their developer community forums.