Steps to Generate Your API ID and Transaction/Signature Key

1. Sign into the Merchant Interface.
2. Select Account from the main toolbar.
3. Under Security Settings, select API Credentials & Keys.
4. Based on the need and integration, select New Transaction Key or New Signature Key.
5. To disable the old Transaction or Signature Key, check the box labeled Disable Old Transaction/Signature Key Immediately.
6. If the Disable Old Transaction/Signature Key check box is not selected, the old Transaction or Signature Key will automatically expire in 24 hours. This will also impact any use of the Signature Key for transaction response validation for the SHA2 field. If the old Transaction/Signature Key is not expired, the previous key will continue to be used for the hash/response validation.
7. Select Submit to continue.
8. Request and enter PIN for verification.
9. Your new Transaction/Signature Key is displayed.

Steps to Generate Your Public Client Key

1. Sign into the Merchant Interface.
2. Select Account from the main toolbar.
3. Under Security Settings, select Manage Public Client Key.
4. To disable the old Public Key, check the box labeled Disable Old Public Key(s).
5. If the Disable Old Public Key(s) check box is not selected, the old Disable Old Public Key(s) will automatically expire in 24 hours. If the old Disable Old Public Key(s) is not expired, the previous key will continue to be used for the hash/response validation.
6. Select Submit to continue.
7. Request and enter PIN for verification.
8. Your new Public Client Key is displayed.

Read more official help page here: https://support.authorize.net/knowledgebase/Knowledgearticle/?code=000001271