I am getting error while i try execute list item by id
ClientContext clientContext = TokenHelper.GetClientContextWithAccessToken(sharepointUrl.ToString(), accessToken);
Web web = clientContext.Web;
clientContext.Load(web);
clientContext.ExecuteQuery();
clientContext.Load(web.CurrentUser);
clientContext.ExecuteQuery();
currentUser = clientContext.Web.CurrentUser.Title;
List _list = web.Lists.GetById(_ListGuid);
clientContext.Load(_list);
clientContext.ExecuteQuery();
Microsoft.SharePoint.Client.ListItem _item = _list.GetItemById(ItemID);
clientContext.Load(_item);
clientContext.ExecuteQuery(); //ERROR HERE
Response.Write(_item["Author"].ToString());
Item does not exist. It may have been deleted by another user.
The problem was in the permission in the manifest file, and while you are deploying the app, SharePoint asks you about "trust" then you have to choose the list which you want to operate with.