1. Log into your Merchant Interface at https://account.authorize.net.
2. Click Settings in the main left side menu.
3. Click API Login ID and Transaction Key.
4. Under Create New Transaction Key, enter your Secret Answer.
Note: When obtaining a new Transaction Key, you may choose to disable the old Transaction Key by clicking on the box titled, Disable Old Transaction Key(s). You may want to do this if you suspect your previous Transaction Key is being used fraudulently.
5. Click Submit.
If the "Disable Old Transaction Key(s)" box is not checked, the old transaction key will automatically expire in 24 hours. When the box is checked, the transaction key would expire immediately.
Be sure to store the Transaction Key in a very safe place. Do not share it with anyone, as it is used to protect your transactions.
The system generated Transaction Key is similar to a password and is used to authenticate requests submitted to the gateway. If a request cannot be authenticated using the Transaction Key, the request is rejected. You may generate a new Transaction Key as often as needed.