Parts of code:

public void Login()
    {
        var request = new LoginWithCustomIDRequest
        {
            CustomId = SystemInfo.deviceUniqueIdentifier,
           
            CreateAccount = true,

            InfoRequestParameters = new GetPlayerCombinedInfoRequestParams
            {
                GetPlayerProfile = true
            }



        };

        PlayFabClientAPI.LoginWithCustomID(request, OnSuccess, OnError);
        
    }



public void OnError(string error, CallRequestContainer reqContainer)
        {
            reqContainer.JsonResponse = error;
            if (reqContainer.ErrorCallback != null)
            {
                reqContainer.Error = PlayFabHttp.GeneratePlayFabError(reqContainer.ApiEndpoint, reqContainer.JsonResponse, reqContainer.CustomData);
                PlayFabHttp.SendErrorEvent(reqContainer.ApiRequest, reqContainer.Error);
                reqContainer.ErrorCallback(reqContainer.Error);
            }
        }
    }


 if (!string.IsNullOrEmpty(www.error))
            {
                OnError(www.error, reqContainer);
            }
            else
            {
                try
                {
                    byte[] responseBytes = www.downloadHandler.data;
                    string responseText = System.Text.Encoding.UTF8.GetString(responseBytes, 0, responseBytes.Length);
                    OnResponse(responseText, reqContainer);
                }
                catch (Exception e)
                {
                    OnError("Unhandled error in PlayFabUnityHttp: " + e, reqContainer);
                }
            }
            www.Dispose();
        }