Why do i get Bad Request when I try to upload an image

Code (CSharp):

1.  
2. WWWForm form = new WWWForm();
3.         byte[] bytes = userData.avatar.EncodeToPNG();
4.  
5.         //form.AddBinaryData("[user]avatar", FileSystemScript.Instance.LoadFile("Application.persistentDataPath/TestFolder/ImageTest"));
6.         form.AddBinaryData("[user]avatar", bytes,"testImage.png","image/png");
7.         form.AddField("[user]first_name", userData.first_name);
8.         form.AddField("[user]last_name", userData.last_name);
9.         form.AddField("_method", "put");
10.  
11.         using (UnityWebRequest www = UnityWebRequest.Put(url, form.data))
12.         {
13.             www.SetRequestHeader("content-type", "application/x-www-form-urlencoded");
14.             www.SetRequestHeader("access-token", authentication.token);
15.             www.SetRequestHeader("client", authentication.client);
16.             www.SetRequestHeader("uid", authentication.uid);
17.  
18.             //www.uploadHandler.contentType = "multipart/form-data";
19.             //www.uploadHandler = new UploadHandlerRaw(System.Text.Encoding.UTF8.GetBytes(jsonData));
20.  
21.             yield return www.SendWebRequest();
22.  
23.             if (www.isNetworkError || www.isHttpError)
24.             {
25.                 Debug.Log("THERE IS ERROR " + www.error);
26.             }
27.             else
28.             {
29.                 if (www.isDone)
30.                 {
31.                     string jsonResult = System.Text.Encoding.UTF8.GetString(www.downloadHandler.data);
32.                     Debug.Log("Server Put Response" + jsonResult);
33.  
34.                     if (jsonResult.Contains("error"))
35.                     {
36.                         Debug.Log("Error Received : " + jsonResult);
37.                     }
38.                     else
39.                     {
40.                     }
41.                 }
42.             }
43.         }