download_zip

That link is working. The endpoint URL is cut off, but it looks like you are referring to using /2/files/download_zip, and you're using curl to call it. I see you're setting 'CURLOPT_FILE' to send the result to a local file. You may want to use different curl options to put the result in memory instead of the local filesystem, and then pass that down to the browser using whatever web framework mechanism is available to you.

The curl library and whatever web framework you're using, if any, aren't made by Dropbox though so we can't provide support for those. I recommend referring to the documentation for those for information on configuring them.