问从Firebase函数创建谷歌云任务抛出错误:3 INVALID_ARGUMENT: Task.payload_type is not set

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Error: 3 INVALID_ARGUMENT: Task.payload_type is not set.
at Object.callErrorFromStatus (D:\programming\AndroidStudioProjects\TWILY\firebaseBackend\functions\node_modules\@grpc\grpc-js\build\src\call.js:31:26)
at Object.onReceiveStatus (D:\programming\AndroidStudioProjects\TWILY\firebaseBackend\functions\node_modules\@grpc\grpc-js\build\src\client.js:180:52)
at Object.onReceiveStatus (D:\programming\AndroidStudioProjects\TWILY\firebaseBackend\functions\node_modules\@grpc\grpc-js\build\src\client-interceptors.js:336:141)
at Object.onReceiveStatus (D:\programming\AndroidStudioProjects\TWILY\firebaseBackend\functions\node_modules\@grpc\grpc-js\build\src\client-interceptors.js:299:181)
at D:\programming\AndroidStudioProjects\TWILY\firebaseBackend\functions\node_modules\@grpc\grpc-js\build\src\call-stream.js:160:78
at processTicksAndRejections (internal/process/task_queues.js:77:11)

const project = JSON.parse(process.env.FIREBASE_CONFIG).projectId;
const location = "europe-west1";
const queue = "message-queue";

const tasksClient = new CloudTasksClient();
const queuePath = tasksClient.queuePath(project, location, queue);
console.log(queuePath);

const url = `https://${location}-${project}.cloudfunctions.net/sendMessageCallback`;

const task = {
  httpRequest: {
    httpMethod: "POST",
    url: url,
    body: Buffer.from("Hello there").toString("base64"),
    headers: {
      "Content-Type": "text/plain",
    },
  },
  scheduleTime: {
    seconds: scheduleSendSeconds,
  },
};

const taskRequest = {parent: queuePath};
taskRequest["task-" + scheduleSendMillis.toString()] = task;
console.log(taskRequest);

return tasksClient.createTask(taskRequest);