Hmm I have a weird issue:

const myTask = task.checkStatus({ taskId: "my-task-id" });
if (myTask) {
   const percent = myTask.getPercentageCompleted();
}

and I get the following error on that

const percent

line:

{
  "type": "error.SuiteScriptError",
  "name": "TypeError",
  "message": "Cannot find function undefined in object version2.SuiteScriptEngineImplV2@68ba1c78.",
  "stack": [
    "createError(N/error)",
    "post(pay_bills_restlet.js:31)",
    "createError(N/error)"
  ],
  "cause": {
    "message": "Cannot find function undefined in object version2.SuiteScriptEngineImplV2@68ba1c78.",
    "fileName": "pay_bills_restlet.js",
    "lineNumber": 31,
    "name": "TypeError",
    "stack": "\tat pay_bills_restlet.js:31 (post)\n\tat INVOCATION_WRAPPER$sys:27 (restletwrapper)\n\tat INVOCATION_WRAPPER$sys:38\n\tat INVOCATION_WRAPPER$sys:21\n\tat INVOCATION_WRAPPER$sys:45\n\tat INVOCATION_WRAPPER$sys:1\n",
    "rhinoException": "org.mozilla.javascript.EcmaError: TypeError: Cannot find function undefined in object version2.SuiteScriptEngineImplV2@68ba1c78. (pay_bills_restlet.js#31)"
  },
  "notifyOff": false,
  "userFacing": true
}