如题：在NativePayService中封装的预下单，url是固定的，通过配置hostName也仅可以更改成hk的域名，那怎么开启沙箱环境呢？

在postman中直接请求https://api.mch.weixin.qq.com/xdc/apiv2sandbox/v3/pay/transactions/native，提示商户号非法，我是否可以认为沙箱中可以测试这个v3接口呢？

puPrepayResponse prepay(PrepayRequest request) {
  String requestPath = "https://api.mch.weixin.qq.com/v3/pay/transactions/native";
  PrepayRequest realRequest = request;
  if (this.hostName != null) {
    requestPath = requestPath.replaceFirst(HostName.API.getValue(), hostName.getValue());
  }
  HttpHeaders headers = new HttpHeaders();
  headers.addHeader(Constant.ACCEPT, MediaType.APPLICATION_JSON.getValue());
  headers.addHeader(Constant.CONTENT_TYPE, MediaType.APPLICATION_JSON.getValue());
  HttpRequest httpRequest =
      new HttpRequest.Builder()
          .httpMethod(HttpMethod.POST)
          .url(requestPath)
          .headers(headers)
          .body(createRequestBody(realRequest))
          .build();
  HttpResponse httpResponse =
      httpClient.execute(httpRequest, PrepayResponse.class);
  return httpResponse.getServiceResponse();
}