Easyshop | Commerce solution for Plone | Frontend Framework library

I want to fetch some data from the server by using the retrofitlibrary on RecyclerView but the data is not showing on RecycleView. I read lots of answers but did not solve it yet so please solve my problem thank you in advance.

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I am writing android app with firebase DB and testing it on android api 22 and it's work, but when I try to launch it on api 26 (xiaomi mi 6) it's terminating. I guess the problem is with Gson().fromJson().

Error with api 26:

There is no problem in getting the value in textbox for username and email but i am having the problem in getting the rendered value i.e Rolename in the dropdown list. //Controller class public JsonResult GetByID(int ID) { var user = userRepo.GetAllUsers().Find(x => x.UserID.Equals(ID)); return Json(user, JsonRequestBehavior.AllowGet); }