Probably something dumb on my part, but I can't seem to get connected to Authorize.net - either their real gateway or test account.
Authorize.net has a sandbox/test arena that you access through their test mechanism, so you sign up for a test account and they give you a test LoginID and Transaction Key. They confirmed that you access the test account through the same gateway as what's in the Shop Settings->Payment grid: https://test.authorize.net/gateway/transact.dll. I put in my "test" ID and Transaction Key there as well. For the checkout page, I changed the ec_PaymentMethod field to have "Credit Card...authorize.net" first, then "Bankwire...bankwire" second. No PayPal while testing.
Can you help me with what I'm missing and/or can otherwise try?