Making a plugin with SetHome
I need to implement a check for the player to be in the List

I explain when a player uses a teleport, I add it to List<T>

private readonly List<ulong> UserIdTP = new List<ulong>(); //   Here I created a field where the player will be stored

Further after the teleport, I add it there

UserIdTP.Add(userid);

And I start the timer which, after the expiration, delete it from there

timer.Once(cfg.timetpPlayer, () =>  UserIdTP.Remove(userid));

Now I need to make a check, if the timer has not expired, and the player is in the List, then he is forbidden to use the teleport

                if(UserIdTP.Contains(userid))
                {
                 ShowUI(player,$"Телепорт не доступен: {cfg.timetpPlayer} сек.");
                 return;

Unfortunately it doesn't work, what's the problem?