API ID uniquely identifies your account to the payment gateway when transactions are submitted.
This API ID is supplied by Authorize.Net when you set up your account with them.
This API ID is separate from your ID to Authorize.Net's "Merchant Interface", although in some cases it may be the same.
If you change your API ID, you must immediately change it to the same value here as well.
Transaction Key is a 16-character randomly-generated password used with your API ID to authenticate your account as an authorized Authorize.Net user when transactions are submitted.
Authorize.Net Test POST URL is the URL assigned by Authorize.Net to be used for test transactions.
Authorize.Net Production POST URL is the URL assigned by Authorize.Net to be used for live transactions.
Note: You can only configure the settings for Address Verification Service (AVS) and Credit Card Security Code (CSC) checks for Authorize.Net on their E-commerce Account Details "Merchant Interface" website, so those fields are not included on this page.