Invalid or missing activities in HTTP body - error as a response to

We are trying to connect Unity app with Chatbot using https://github.com/tompaana/bot-direct-line-for-unity. Starting a new conversation with bot is working properly, but when I try to send a message to it, instead of getting a response I end up with error attached below. Bot is working properly with web/skype, only problem we have is our unity implementation.

I wonder what we are missing in the POST in order to receive a proper response from bot.

Because Unity is somewhat missing features like Network/XHR from browsers developer toolkit, we used Fiddler to get those results:

here is POST sent to chatbot:

POST https://directline.botframework.com/v3/directline/conversations/CRar7Qz6VaEmIeMR6UmUC/activities HTTP/1.1
Host: directline.botframework.com
User-Agent: UnityPlayer/2017.3.1f1 (UnityWebRequest/1.0, libcurl/7.51.0-DEV)
Accept: */*
Accept-Encoding: identity
Transfer-Encoding: chunked
Authorization: Bearer XXX.edited_out.XXX
Content-Type: application/json
X-Unity-Version: 2017.3.1f1

76
{ "type": "message", "channelId": "directline", "from": { "id": "default-user", "name": "User" }, "text": "message text" }
0

here is the response:

HTTP/1.1 400 Bad Request
Cache-Control: no-cache
Pragma: no-cache
Content-Length: 116
Content-Type: application/json; charset=utf-8
Expires: -1
Server: Microsoft-IIS/10.0
Request-Context: appId=cid-v1:91e46abb-4ce5-4d98-9375-02378f649011
X-Powered-By: ASP.NET
Strict-Transport-Security: max-age=31536000
Date: Tue, 15 May 2018 10:21:11 GMT

{
  "error": {
    "code": "MissingProperty",
    "message": "Invalid or missing activities in HTTP body"
  }
}

I'd like to know what we are missing in this POST.

Solution

In older version API, the default value of UnityWebRequest.chunkedTransfer property is true, as you mentioned, to prevent it, we can explicitly set:

UnityWebRequest.chunkedTransfer = false;

Besides, in the latest version, the default value of UnityWebRequest.chunkedTransfer property is false. So if upgrade and use the latest version, it might not cause this issue.