I see you're getting a 400 error code, but you should also print out the response body itself, as it would contain a more useful error message. We can't provide support for the Nemerio OAuth library itself though, as it's not made by Dropbox.
Also, if you want the metadata for any particular file or folder, you should instead call /2/files/get_metadata.
By the way, do not share or post your access token. (This one is short-lived though, and would've expired by now, but it looks like you didn't post the whole thing anyway.)