Learn how to upload any Google Drive file to your Dropbox folder using Google Apps Script. To get started, create a new Dropbox app, as explained in the previous Dropbox example, and get the access token to skip the OAuth2 workflow.

Also see: Upload Drive Files to Google Cloud Storage

function uploadGoogleFilesToDropbox(googleDriveFileId) {
  var parameters = {
    path: '/PDF/labnol.pdf',
    mode: 'add',
    autorename: true,
    mute: false,
  };

  // Add your Dropbox Access Token
  var dropboxAccessToken = 'labnolorg-MZmqX';

  var headers = {
    'Content-Type': 'application/octet-stream',
    Authorization: 'Bearer ' + dropboxAccessToken,
    'Dropbox-API-Arg': JSON.stringify(parameters),
  };

  var driveFile = DriveApp.getFileById(googleDriveFileId);

  var options = {
    method: 'POST',
    headers: headers,
    payload: driveFile.getBlob().getBytes(),
  };

  var apiUrl = 'https://content.dropboxapi.com/2/files/upload';
  var response = JSON.parse(UrlFetchApp.fetch(apiUrl, options).getContentText());

  Logger.log('File uploaded successfully to Dropbox');
}