System.Collections.Generic.List`1[System.String]" JSON error - json

Question

I'm trying to use JSON and I was use PostMan to return Response
this error happent
System.Collections.Generic.List`1[System.String]"}
public ActionResult SendVFCode(string Phone_Number)
{
var jsonSerialiser = new JavaScriptSerializer();
string error = "";
var SearchData ="";
if (Phone_Number == null)
{
error = "Must enter your phone number";
}
else if ( (db.PhoneNumbers.Select(x =>x.Id).Count() < 0)
&& (db.Assistant.Select(x =>x.Id).Count()) < 0)
{
error = "There are no data or your account is not activated";
}
else
{
SearchData = db.PhoneNumbers.Include(x => x.Assistant)
.Where(x => x.PhoneNumber == Phone_Number
&& x.Assistant.IsActive == true).Select(xx =>xx.PhoneNumber).ToList().ToString();
}
json = new
{
err = error,
ResultSearchData = SearchData
};
return Content(jsonSerialiser.Serialize(json));
}

Answer 1

SearchData is not a string. Don't declare it as string and don't try to shove a string into it. It's a List (probably of type List<string> or whatever your Phonenumber type is).
var SearchData =""
Should be:
List<string> SearchData;
And your database call should end in .ToList(), not .ToList().ToString().

Answer 2

Note that ToList() followed with ToString() returns fully-qualified name of the list instead of the list contents, hence you should use List<string> to hold result strings (also the list must be instantiated first before used inside if-block). The correct setup should be like this:
public ActionResult SendVFCode(string Phone_Number)
{
var jsonSerialiser = new JavaScriptSerializer();
string error = "";
var SearchData = new List<string>(); // instantiate list of strings
var phoneCount = db.PhoneNumbers.Select(x => x.Id).Count();
var assistantCount = db.Assistant.Select(x => x.Id).Count();
if (Phone_Number == null)
{
error = "Must enter your phone number";
}
else if (phoneCount < 0 && assistantCount < 0)
{
error = "There are no data or your account is not activated";
}
else
{
// assign list from query results
SearchData = db.PhoneNumbers.Include(x => x.Assistant)
.Where(x => x.PhoneNumber == Phone_Number && x.Assistant.IsActive == true)
.Select(xx => xx.PhoneNumber).ToList();
}
var json = new
{
err = error,
ResultSearchData = SearchData
};
return Content(jsonSerialiser.Serialize(json));
}