[C#] WCF + UserName validation

[SheenBR]

I'm trying for a few days to add username validation in my WCF service. The class starting the server:

         public static void Run(System.Net.IPAddress IP)
        {
            var host = new ServiceHost(typeof(Pipes), new Uri[] { new Uri("net.tcp://" + IP.ToString()) });

            var p = new NetTcpBinding(SecurityMode.Message);
            p.Security.Message.ClientCredentialType = MessageCredentialType.UserName;
            
            host.Credentials.UserNameAuthentication.UserNamePasswordValidationMode = System.ServiceModel.Security.UserNamePasswordValidationMode.Custom;
            host.Credentials.UserNameAuthentication.CustomUserNamePasswordValidator = new Validator();


            host.AddServiceEndpoint(typeof(IMasterServer), p, "MasterServer");
            host.AddServiceEndpoint(typeof(IDatabaseService), p, "DatabaseServer");
            host.AddServiceEndpoint(typeof(IChatServer), p, "ChatServer");

            host.Open();
        } 
  

but when I try to run, an error occurs:

The ChannelDispatcher at 'net.tcp://127.0.0.1/MasterServer' with contract(s) 'IMasterServer' is unable to open its IChannelListener.

Validator class:

     public class Validator : UserNamePasswordValidator
    {
        public override void  Validate(string userName, string password)
        {
             
        }
    } 
  

no codes because I couldnt fix the error yet =/

what am I doing wrong? I already looked tons of articles on msdn, codeproject but either they are very confused using app.config files or they arent exactly what I was looking for...

It says also that I need to specify a service certificate in servicecredentials.. how?