TIKTOK API - Generate Access Token error message: 'Timestamp has expired.'

Question

I am trying to pull tiktok data from the TikTok AP, and I am experiencing two problems currently:

1. I am having the error message: 'Timestamp has expired' even though I just renewed a new authentication code. I tried generating a timestamp dynamically to avoid this error but it is not working.

var timestamp = Math.floor(Date.now() / 1000).toString(); // Generate timestamp in seconds

2. I'm not sure if I am meeting the timestamp format requirements of the TikTok API and I don't know where to find this format as well.

If anyone could provide some advice on the above 2 points it would help a lot! Posting my code below for reference

function getToken() {
  try {
    var url = 'https://business-api.tiktok.com/open_api/v1.3/oauth2/creator_token/?business=tt_user';
    var clientId = '';
    var clientSecret = '';
    var authCode = '';

    //var timestamp = Math.floor(Date.now() / 1000).toString(); // Generate timestamp in seconds

    var options = {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
        //'Timestamp': timestamp
      },
      payload: JSON.stringify({
        "business": "tt_user",
        "client_id": clientId,
        "client_secret": clientSecret,
        "grant_type": "authorization_code",
        "auth_code": authCode,
      })
    };

    const response = UrlFetchApp.fetch(url, options);
    const responseData = response.getContentText();
    const dateHeader = response.getHeaders()['Date'];

    const data = JSON.parse(responseData);
}

If there are any fundamental issues with the base code, I would love some feedback.