支付宝当面付申请支付

支付宝当面付的代码，

返回
{"alipay_trade_refund_response":{"code":"40002","msg":"Invalid Arguments","sub_code":"isv.invalid-signature-type","sub_msg":"无效签名类型"},"sign":"8c5219140da91b30a44defcb880545b2"}
求大神支招

http://jingyan.baidu.com/article/066074d655db34c3c21cb088.html