Follow these instructions to locate the necessary API account credentials needed to activate Authorize.net CIM and eCheck: 


1. Login to your Authorize.net account and go to Account → Settings → API Credentials & Keys

2. On this page you can locate your API Login ID

3. To obtain your Transaction Key, go to the section on the page titled, “Create New Transaction Key” and enter the answer to your security question

4. Once you have both your API Login ID and Transaction Key, login to your Magento admin panel and go to System → Configuration → Payment Methods → Authorize.Net CIM → General Settings and enter your API credentials and click Save

5. You can verify that your credentials are correct if the Status under General Information for Authorize.Net payment method says Connected successfully