迁移到Laravel 5.1后，Authorize.net返回E00006

Question

我将我的网站从laravel 4.2迁移到laravel 5.1。但迁移后，我的支付网关（authorize.net）已停止工作。我使用authorize.net SDK V1.8 for php。以下是来自authorize.net的回复 -

AuthorizeNetCIM_Response Object
(
    [xml] => SimpleXMLElement Object
        (
            [messages] => SimpleXMLElement Object
                (
                    [resultCode] => Error
                    [message] => SimpleXMLElement Object
                        (
                            [code] => E00006
                            [text] => The API user name is invalid or not present.
                        )

                )

        )

    [response] => ErrorE00006The API user name is invalid or not present.
    [xpath_xml] => SimpleXMLElement Object
        (
            [messages] => SimpleXMLElement Object
                (
                    [resultCode] => Error
                    [message] => SimpleXMLElement Object
                        (
                            [code] => E00006
                            [text] => The API user name is invalid or not present.
                        )

                )

        )

)

任何人都可以解释一下这个错误究竟意味着什么＆＃34; API用户名无效或不存在。＆＃34;以及如何解决这个问题？