Using binary utf_8 to upload files give code 500

I am trying to upload a binary utf_8 file with content-type: 'application/octet-stream'

I am getting code 500 as response 

{
   type: "http.ClientResponse",
   code: 500,
   headers: {
      "Transfer-Encoding": "chunked",
      "X-Dropbox-Request-Id": "640a364369e1655286244898d330da00",
      "X-Robots-Tag": "noindex, nofollow, noimageindex",
      Server: "nginx",
      "Content-Security-Policy": "sandbox allow-forms allow-scripts",
      Date: "Tue, 15 Oct 2019 08:28:50 GMT",
      "Content-Type": "text/plain; charset=utf-8",
      Via: "1.1 mono002"
   },
   body: ""
}

How do is send binary utf-8 pdf files to dropbox?