OracleDependency

I want to make an application that has push notifications, using OracleDependency, I follow the instructions in the documentation.

I execute the following commands:

grant change notification to SN_Hospitales;
GRANT EXECUTE ON DBMS_CHANGE_NOTIFICATION TO SN_Hospitales;

and I have the following code:

 var Entidad= "sn_hospitales.entidad_dependency";
        var login = "DATA SOURCE=(DESCRIPTION = " +
                    " (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.54.170) 
(PORT = 1521)) " +
                    " (CONNECT_DATA = " +
                    " (SERVER = DEDICATED) " +
                    " (SERVICE_NAME = SERUD) " +
                    " ))   ; USER ID=SN_Hospitales;PASSWORD=XXXXXX";



        OracleConnection con = new OracleConnection(login);
        con.Open();
        OracleDependency dependency = new OracleDependency();
        OracleCommand cmd = con.CreateCommand();
        string sql = "select nombre from " + Entidad;
        cmd.CommandText = sql;
        dependency.OnChange += new OnChangeEventHandler(dep_OnChange);
        dependency.AddCommandDependency(cmd);
        cmd.Notification.IsNotifiedOnce = false;
        cmd.AddRowid = true;
        cmd.ExecuteNonQuery();

But it does not work, can someone help me if I leave something or something has to be done in the Oracle?

thanks