API Login ID
You can find your unique API Login ID by clicking on the 'Account' link at the Authorize.Net Merchant Interface. Then click 'API Login ID and Transaction Key'. Your API Login ID will be displayed.
You can find your unique Transaction Key by clicking on the 'Account' link at the Authorize.Net Merchant Interface. Then click 'API Login ID and Transaction Key'. For security reasons, you cannot view your Transaction Key, but you will be able to generate a new one.