I was experiencing this issue with 20182.2f1. The work around for the Post method shown here fixed it for me:

https://codetolight.wordpress.com/2017/01/18/unity-rest-api-interaction-with-unitywebrequest-and-besthttp/

Just remember to add an Access Token to the request header if you need to.

I still get this on 2018.2.6f1. Setting chunk false does not do any good. Any workarounds?

I am using Unity3d 2017.4.2f2 and I am getting this error as well.
Following is my HTTP POST request:

List<IMultipartFormSection> formData = new List<IMultipartFormSection>();
formData.Add(new MultipartFormDataSection("email="+email+"&amp;name="+name));
UnityWebRequest www = UnityWebRequest.Post(Utility.BASE_URL + Utility.LOGIN, formData);
www.chunkedTransfer = false;
yield return www.SendWebRequest();

if (www.isNetworkError || www.isHttpError)
{
Debug.Log(www.error);
}
else
{
Debug.Log(www.downloadHandler.text);

}

This is not fixed in 2017..3.1p4 either. I tried all workarounds in this thread with no luck. I get a Generic/unknown HTTP error while it's works with Postman.

This is not fixed in 2017..3.1p2

I use UnityWebRequest and I am on 2017.4.0f1, and I have tried all work arounds from different forums. From changing chunkedTransfer to false, Using Put, but changing the method to "POST", Adding .SetRequestHeader ("X-HTTP-Method-Override", method), trying uploadhandler and downloadhandler. I tried sending raw JSON on Postman and the request was received but in Unity, it just gives me "Generic/unknown HTTP error". Please help.

Figured this out and it works now! Version 2017.3.1f1. Here's the code:

string accessUri = "";
string data1 = "";
string data2 = "";

WWWForm form = new WWWForm();
form.AddField("data1", data1);
form.AddField("data2", data2);

using (UnityWebRequest www = UnityWebRequest.Post(accessUri, form)) {
yield return www.SendWebRequest();

if (www.isNetworkError || www.isHttpError) {
Debug.Log(www.error);
} else {
Debug.Log("Form upload complete!");
}
}

@ARESUNDNES - Can you post your code as an example? I tried www.chunkedTransfer = false; and am still getting the error.

The issue is resolved for me by setting chunkedTransfer to false:

```
UnityWebRequest www = UnityWebRequest.Post(url, formData);
www.chunkedTransfer = false;
```

Not fixed. Still get in 2017.4.0f1