LifterLMS Authorize.Net stores requires the Transaction Details API to be enabled in your Authorize.Net account in order to process refunds from an within your WordPress admin panel.
If you are seeing the following error message while attempting to process a refund you must enable the Transaction Details API to process refunds:
Unable to process Authorize.Net refunds: Transaction Details API is not enabled for you account.
To enable the API, you’ll need to log in to your Authorize.Net account dashboard and turn the API on with the click of a button. Full details on how to do so are available from Authorize.Net.
Once you’ve enabled the API you will be able to process refunds from LifterLMS via the API.