Paypal在交易时抛出错误

Question

我使用以下代码进行交易：

try
            {
                //create request and add headers
                $params = array("http" => array(
                    "method" => "POST",                                                 
                    "content" => $body_data,                                             
                    "header" =>  "X-PAYPAL-SECURITY-USERID: " . $API_UserName . "\r\n" .
                         "X-PAYPAL-SECURITY-SIGNATURE: " . $API_Signature . "\r\n" .
                         "X-PAYPAL-SECURITY-PASSWORD: " . $API_Password . "\r\n" .
                         "X-PAYPAL-APPLICATION-ID: " . $API_AppID . "\r\n" .
                         "X-PAYPAL-REQUEST-DATA-FORMAT: " . $API_RequestFormat . "\r\n" .
                         "X-PAYPAL-RESPONSE-DATA-FORMAT: " . $API_ResponseFormat . "\r\n"
                ));

                //create stream context
                $ctx = stream_context_create($params);

                //open the stream and send request
                $fp = @fopen($url, "r", false, $ctx);

                //get response
                $response = stream_get_contents($fp);

                //check to see if stream is open
                 if ($response === false) {
                    throw new Exception("php error message = " . "$php_errormsg");
                 }

                //close the stream
                 fclose($fp);

我已经检查了所有与paypal相关的详细信息并且它们似乎是正确的，但是当我尝试点击立即购买时，它会抛出错误

＆＃34; 此交易无效。请返回收件人的网站，然后重试。＆＃34;

我不知道什么是错误的，它曾经工作过，但突然间它停止了工作并抛出了上述错误。