小程序预签约：https://pay.weixin.qq.com/doc/v3/merchant/4012525209

返回错误： 500 Internal Server Error: "{"code":"SYSTEM_ERROR","message":"系统繁忙，请稍后重试"}

我的部分请求

String url = "https://api.mch.weixin.qq.com/v3/papay/scheduled-deduct-sign/contracts/pre-entrust-sign/mini-program";
String urlPath = "/v3/papay/scheduled-deduct-sign/contracts/pre-entrust-sign/mini-program";

Map<String, Object> requestBody = new HashMap<>();
requestBody.put("appid", request.getAppid());
requestBody.put("openid", request.getOpenid());
requestBody.put("plan_id", request.getPlanId());
requestBody.put("out_contract_code", request.getContractCode());
requestBody.put("contract_display_account", request.getContractDisplayAccount());
requestBody.put("contract_notify_url", request.getNotifyUrl());
requestBody.put("description", request.getDescription());

HttpEntity<String> requestEntity = new HttpEntity<>(requestBodyJson, headers);
ResponseEntity<String> response = restTemplate.exchange(url, HttpMethod.POST, requestEntity, String.class);

想问一下是权限不足，还是请求参数有误，或者是其他什么问题？