微信退款问题

public function Home_index(){
$ref= md5("appid=wx4654546&mch_id=1278391239&nonce_str=2194kfhaafaf384&op_user_id=646131"
. "&out_refund_no=D2131231&out_trade_no=1231jaf&refund_fee=0.01&total_fee=0.01"
. "&transaction_id=1293102u4slfk14&key=asduaisd12739182");//sign加密MD5

$refund=array(
'appid'=>'1',
'mch_id'=>'1',//商户号
'nonce_str'=>'1',//随机字符串
'op_user_id'=>'1',
'out_refund_no'=>'1',
'out_trade_no'=>'1',
'refund_fee'=>'1',
'total_fee'=>'1',
'transaction_id'=>'1',
'sign'=>$ref


);

$url="https://api.mch.weixin.qq.com/secapi/pay/refund";;//微信退款地址，post请求
$xml=arrayToXml($refund);


$ch=curl_init();
curl_setopt($ch,CURLOPT_URL,$url);
curl_setopt($ch,CURLOPT_HEADER,1);
curl_setopt($ch,CURLOPT_RETURNTRANSFER,1);
curl_setopt($ch,CURLOPT_SSL_VERIFYPEER,1);//证书检查
curl_setopt($ch,CURLOPT_SSLCERTTYPE,'pem');
curl_setopt($ch,CURLOPT_SSLCERT,dirname(__FILE__).'/WxPayPubHelper/cacert/apiclient_cert.pem');
curl_setopt($ch,CURLOPT_SSLCERTTYPE,'pem');
curl_setopt($ch,CURLOPT_SSLKEY,dirname(__FILE__).'/WxPayPubHelper/cacert/apiclient_key.pem');
curl_setopt($ch,CURLOPT_SSLCERTTYPE,'pem');
curl_setopt($ch,CURLOPT_CAINFO,dirname(__FILE__).'/WxPayPubHelper/cacert/rootca.pem');
curl_setopt($ch,CURLOPT_POST,1);
curl_setopt($ch,CURLOPT_POSTFIELDS,$xml);

$data=curl_exec($ch);
if($data){ //返回来的是xml格式需要转换成数组再提取值，用来做更新
curl_close($ch);
dump($data);
}else{
$error=curl_errno($ch);
echo "curl出错，错误代码：$error"."<br/>";
echo "<a href='http://curl.haxx.se/libcurl/c/libcurs.html'>;错误原因查询</a><br/>";
curl_close($ch);
echo false;
} 
}