Upload documents with post request

  domain: null,
  _events: { end: [Function: bound _clearTimeout] },
  _eventsCount: 1,
  _maxListeners: undefined,
  _agent: false,
  _formData:
   FormData {
     _overheadLength: 163,
     _valueLength: 0,
     _lengthRetrievers: [ [Function] ],
     writable: false,
     readable: true,
     dataSize: 0,
     maxDataSize: 2097152,
     pauseStreams: true,
     _released: false,
     _streams:
      [ '----------------------------703401962293487607875932\r\nContent-Disposition: form-data; name="files[]"; filename="Objective.pdf"\r\nContent-Type: application/pdf\r\n\r\n',
        [Object],
        [Function: bound ] ],
     _currentStream: null,
     _events: { error: [Function: bound ] },
     _eventsCount: 1,
     _boundary: '--------------------------703401962293487607875932' },
  method: 'POST',
  url: 'https://sandbox.e-signlive.com/api/packages/7d6ed628-1d3f-4110-8b2b-87645da3cb04/documents',
  _header:
   { 'user-agent': 'node-superagent/1.8.3',
     accept: 'application/json',
     'content-type': 'multipart/form-data',
     authorization: 'Basic #####################' }, //my api key
  header:
   { 'User-Agent': 'node-superagent/1.8.3',
     Accept: 'application/json',
     'Content-Type': 'multipart/form-data',
     Authorization: 'Basic ######################' }, //my api key
  writable: true,
  _redirects: 0,
  _maxRedirects: 5,
  cookies: '',
  qs: {},
  qsRaw: [],
  _redirectList: [],
  _streamRequest: false

{ [Error: cannot POST /api/packages/7d6ed628-1d3f-4110-8b2b-87645da3cb04/documents (406)]
  status: 406,
  text: '{"dirtyFields":["messageKey","code","technical","name","message"],"packageId":null,"technical":"","messageKey":"http.status.406","entity":null,"message":"[http.status.406]","code":406,"name":"Unhandled Server Error"}',
  method: 'POST',
  path: '/api/packages/7d6ed628-1d3f-4110-8b2b-87645da3cb04/documents' }