const r = await mn.api('/document-export-plans/' + planId + '/discard', {
  method: 'POST',
  body: { confirm: true }
});
if (r.error) mn.log(r.error.code);

{
  "planId": "plan-3F1A2B40",
  "state": "ready",
  "exportId": "export-7C2D9E10",
  "exportRoute": "/documents/8daef026/export",
  "downloadRoute": "/document-exports/export-7C2D9E10/file",
  "selectedPageCount": 12,
  "progress": 1
}

{
  "error": {
    "code": "NOT_FOUND",
    "message": "找不到目标对象。"
  }
}