Getting E00001 in sandbox

[ajpirciovs]

Test mode is off. Using Magento default authorize.net module. No matter what I do with my settings (with or without test mode) I get this as my cURL response:

{"messages":{"resultCode":"Error","message":[{"code":"E00001","text":"Unexpected character encountered while parsing value: x. Path '', line 0, position 0."}]}}

[ajpirciovs]

Ok so I'm dumb. For anyone else that stumbles into this. Magento 1.9.x uses a deprecated endpoint. I was putting in the endpoint for the new API, and that won't work.

Make sure you are using: https://test.authorize.net/gateway/transact.dll if you are using a new sandbox account with magento 1.9.x