Replying to previous tweet not working

[weareblahs]

I followed the docs and tweeted successfully with API v2 using my own keys, but using the following script (snippet):

  const firstTweet = await twitterClient.v2.tweet(tweet1);
  await twitterClient.v2.reply(tweet2, firstTweet.id);

does not work when replying to the first tweet. Instead, it returns a 403 error with this:

{
  "errors": [
    {
      "parameters": {
        "$.reply": [
          "{}"
        ]
      },
      "message": "$.reply.in_reply_to_tweet_id: is missing but it is required"
    }
  ],
  "title": "Invalid Request",
  "detail": "One or more parameters to your request was invalid.",
  "type": "https://api.twitter.com/2/problems/invalid-request"
}

I'm not sure what's the issue. for twitterClient.v2.reply(tweet, in_reply_to), it should take these 2 values as expected. Is this a bug or is there any problems in my code?