This error indicates that a "User Login ID" and not an "API Login ID" is being used to connect DPD to Autorize.net. For example, if an Account Owner, Account Administrator, Transaction Manager, or Account Analyst login ID is used for the DPD payment method setup, this error will occur.
To resolve this issue, the API Login ID and Transaction Key need to be used to properly connect DPD to Authorize.Net. The API Login ID can be obtained by following these steps:
1) Log into the Merchant Interface at https://account.authorize.net.
2) Click Settings in the main left side menu.
3) Click API Login and Transaction Key.
If an API Login ID needs to be configured, this page is where the option exists. If an API login ID has already been configured, it will be visible here.