When I attempt to upload an attachment to Freshdesk with chunked Transfer-Encoding, the request fails. It appears that you are running an outdated version of the nginx proxy that does not support chunked Transfer-Encoding (http://serverfault.com/questions/164220/is-there-a-way-to-avoid-nginx-411-content-length-required-errors).
curl -u firstname.lastname@example.org:password --header "Transfer-Encoding: chunked" -F "helpdesk_note[attachments][resource]=@/path/to/file.jpg" -F "helpdesk_note[body]=Note content" -F "helpdesk_note[private]=false" -X POST https://domain.freshdesk.com/helpdesk/tickets/[id]/conversations/note.json
<head><title>411 Length Required</title></head>
<center><h1>411 Length Required</h1></center>