In my ASP.NET Core (.NET Framework) project, I'm getting above error on my following Controller Action method. What I may be missing? Or, are there any work arounds?:
public class ClientController : Controller
{
    public ActionResult CountryLookup()
    {
        var countries = new List<SearchTypeAheadEntity>
        {
            new SearchTypeAheadEntity {ShortCode = "US", Name = "United States"},
            new SearchTypeAheadEntity {ShortCode = "CA", Name = "Canada"}
        };
        
        return Json(countries, JsonRequestBehavior.AllowGet);
    }
}
UPDATE:
Please note folowing comments from @NateBarbettini below:
JsonRequestBehavior has been deprecated in ASP.NET Core 1.0.return type of action method does not specifically need to be of type JsonResult. ActionResult or IActionResult works too.Returning Json-formatted data:
public class ClientController : Controller
{
    public JsonResult CountryLookup()
    {
         var countries = new List<SearchTypeAheadEntity>
         {
             new SearchTypeAheadEntity {ShortCode = "US", Name = "United States"},
             new SearchTypeAheadEntity {ShortCode = "CA", Name = "Canada"}
         };
         return Json(countries);
    }
}
                        In Code it's replace To JsonRequestBehavior.AllowGet with new Newtonsoft.Json.JsonSerializerSettings()
It's Work same as JsonRequestBehavior.AllowGet
public class ClientController : Controller
{
  public ActionResult CountryLookup()
  {
    var countries = new List<SearchTypeAheadEntity>
        {
            new SearchTypeAheadEntity {ShortCode = "US", Name = "United States"},
            new SearchTypeAheadEntity {ShortCode = "CA", Name = "Canada"}
        };
    return Json(countries, new Newtonsoft.Json.JsonSerializerSettings());
  }
}
                        Some times you need to return a message back in JSON, simply use the JSON result as below, no need for jsonrequestbehavior any more, below simple code to use:
public ActionResult DeleteSelected([FromBody]List<string> ids)
{
    try
    {
        if (ids != null && ids.Count > 0)
        {
            foreach (var id in ids)
            {
                bool done = new tblCodesVM().Delete(Convert.ToInt32(id));
                
            }
            return Json(new { success = true, responseText = "Deleted Scussefully" });
        }
        return Json(new { success = false, responseText = "Nothing Selected" });
    }
    catch (Exception dex)
    {
        
        return Json(new { success = false, responseText = dex.Message });
    }
}
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