Remove duplicate record in list

Question

I have get record by id. It's API run successfully. But i have face issue same record get multiple time

public SupplementResponse GetSupplementsList(SupplemetParam obj_parameter)
{
SupplementResponse obj_result = new SupplementResponse();
List<SupplementListDetail> lst = new List<SupplementListDetail>();
var PDFURL = new ConfigurationBuilder().AddJsonFile("appsettings.json").Build().GetSection("AppSettings")["SupplementUrl"];
try
{
var matchingdata = (from c in _context.TblSupplementDetail
join sc in _context.SupplementMaster on c.SupplementId equals sc.SupplementId
where c.UserId == obj_parameter.UserId
select new
{
sc.SupplementId,
sc.SupplementType,
sc.SupplementPdf,
c.SupplementStatus
}).ToList();
if (matchingdata.Count > 0)
{
foreach (var item in matchingdata)
{
SupplementListDetail obj_supplement = new SupplementListDetail();
obj_supplement.SupplementsId = item.SupplementId;
obj_supplement.SupplementType = item.SupplementType;
obj_supplement.SupplementPDF = PDFURL + "" + item.SupplementPdf;
obj_supplement.SupplementStatus = Convert.ToInt32(item.SupplementStatus);
lst.Add(obj_supplement);
}
}
var Supplement_List = _context.SupplementMaster.ToList();
{
if(Supplement_List .Count >0)
{
foreach (var item in Supplement_List)
{
if(item.SupplementStatus==false)
{
SupplementListDetail obj_supplement = new SupplementListDetail();
obj_supplement.SupplementsId = item.SupplementId;
obj_supplement.SupplementType = item.SupplementType;
obj_supplement.SupplementPDF = PDFURL + "" + item.SupplementPdf;
obj_supplement.SupplementStatus = Convert.ToInt32(item.SupplementStatus);
lst.Add(obj_supplement);
}
}
}
}
obj_result.Response = 1;
obj_result.ErrorMessage = "No Error Found";
List<SupplementListDetail> uniqueLst = lst.Distinct().ToList(); //i have use this here.
obj_result.lst_Supplement = uniqueLst;
It's me classes.
public class SupplemetParam
{
public int UserId { get; set; }
}
public class SupplementResponse
{
public int Response { get; set; }
public string ErrorMessage { get; set; }
public IEnumerable<SupplementListDetail> lst_Supplement { get; set; }
}
public class SupplementListDetail
{
public int SupplementsId { get; set; }
public string SupplementType { get; set; }
public string SupplementPDF { get; set; }
public int SupplementStatus { get; set; }
}