Can't access my YouTube Brand channels via API

Question

I'm trying to get my YouTube Brand channel's live streaming chat data using YouTube Live Streaming API, on Google AppsScript.

I can see list of my Brand channels from this page > https://myaccount.google.com/brandaccounts

I made OAuth2 service and authenticated with my Google account. I can find access token from the service. (code below)

But when I trying to get list of my channels from https://www.googleapis.com/youtube/v3/channels with mine=true, it only returns one of my channels which is not branded one. (Now I deleted that channel and channels API returns no channel)

here's my code:

function getYouTubeService() {
  return OAuth2.createService('YouTube')
    .setAuthorizationBaseUrl('https://accounts.google.com/o/oauth2/auth')
    .setTokenUrl('https://oauth2.googleapis.com/token')
    .setClientId('{my client id of webapp here}')
    .setClientSecret('{my client secret of webapp here}')
    .setCallbackFunction('authCallback')
    .setScope([
      'https://www.googleapis.com/auth/youtube.readonly',
      'https://www.googleapis.com/auth/youtube.force-ssl'
    ])
    .setPropertyStore(PropertiesService.getUserProperties());
}


function getChannelsList() {
  const service = getYouTubeService();
  if (!service.hasAccess()) {
    const authorizationUrl = service.getAuthorizationUrl();
    console.log(service.getAuthorizationUrl());

    return;
  }

  const token = service.getAccessToken();
  
  var url = `https://www.googleapis.com/youtube/v3/channels`
          + `?part=snippet`
          + `&mine=true`
          ;
  const options = {
    method: 'get',
    headers: {
      Authorization: `Bearer ${token}`,
    },
    muteHttpExceptions: true,
  };

  const response = UrlFetchApp.fetch(url, options);
  const data = JSON.parse(response.getContentText());

  console.log(JSON.stringify(data, null, 5));
}

I've spent hours consulting with GPT, trying various tests, keep getting succeeded to get other channel's public statistics using API but cannot reach my brand channels.

I no longer know what else to look at. Please help me.