Authorize.net payment gateway integration in C#

First you'll have to set up a developer test account for you to be able to test the payment processing and functionality. You can sign-up here: https://developer.authorize.net/testaccount/

After that you can try out SIM integration: http://developer.authorize.net/api/sim/

Or choose the best API that best suits your needs here: http://developer.authorize.net/downloads/samplecode/

For more details you can check out the developer home page here: http://developer.authorize.net/