服务端生成的 {"prepay_id":"wx18120927662278be133d62971e64070001“}

params.put("appId", "");  // 应用 ID
params.put("mchid", "");  // 商户号
params.put("prepay_id", "wx18120927662278be133d62971e64070001");  // 服务器返回的 prepay_id
params.put("nonce_str", nonceStr);  // 随机字符串
params.put("timeStamp", String.valueOf(timestamp));  // 随机字符串
String apiKey = "";  // 商户 API 密钥

// 生成客户端签名
String signature = generateClientSignature(params, apiKey);

PayReq req = new PayReq();
req.appId = "";
req.partnerId = "";
req.prepayId = prepayId; // 从回调中获取 prepay_id
req.nonceStr = nonceStr; // 填入随机字符串
req.timeStamp = String.valueOf(timestamp);
req.packageValue = "Sign=WXPay";
req.signType="HmacSHA256";
req.sign = signature;
api.sendReq(req); // 发起支付请求


app调起微信 显示支付签名失败！！！