后台使用的是HMAC-SHA256签名

Android端是这么设置的
PayReq payReq = new PayReq();
 payReq.appId = payEntity.getAppid().trim();
 payReq.partnerId = payEntity.getPartnerid().trim();
 payReq.nonceStr = payEntity.getNoncestr().trim();
 payReq.timeStamp = payEntity.getTimestamp().trim();
 payReq.packageValue = "Sign=WXPay".trim();
 payReq.signType="HMAC-SHA256";
 payReq.prepayId = payEntity.getPrepayid().trim();
 payReq.sign = payEntity.getSign().trim();
 api.sendReq(payReq);

可是结果怎么都是resp.errcode = -1
这是我设置的有问题还是怎么回事