When we tested the recent version of the plugin in our side the plugin is working fine so make sure you have USD in your currency setting and also please recheck the key as the key may be incorrect which may have generated the issue.
If the issue still persists then kindly let us know.
Issue still exists. Verified currency in both the website and on authorize.net
Created a new sandbox account, new API Login ID and new Transaction key.
Still getting the same error, “Failed to Validate Account.”