Getting error- Hard-coded logon parameters not allowed when using a Destination Configuration while connecting to SAP server dynamically

You can try below sample code. I would suggest you to try using this:

public class Program {
   static void Main(string[] args) {
      SapConnection con = new SapConnection();
      RfcDestinationManager.RegisterDestinationConfiguration(con);
      RfcDestination dest = RfcDestinationManager.GetDestination("NSP");
      RfcRepository repo = dest.Repository;

      IRfcFunction fReadTable = repo.CreateFunction("ZSOMA");
      fReadTable.SetValue("I_NRO1", 1);
      fReadTable.SetValue("I_NRO2", 2);
      fReadTable.Invoke(dest);
     
      var result = fReadTable.GetValue("E_RESULT");
      Console.WriteLine(result.ToString());
      Console.ReadLine();
    }
}

public class SapConnection : IDestinationConfiguration {
    public RfcConfigParameters GetParameters(string destinationName) {
       RfcConfigParameters conf = new RfcConfigParameters();
       if (destinationName == "NSP") {
           conf.Add(RfcConfigParameters.AppServerHost, "sap-vm");
           conf.Add(RfcConfigParameters.SystemNumber, "00");
           conf.Add(RfcConfigParameters.SystemID, "xxx");
           conf.Add(RfcConfigParameters.User, "yourusername");
           conf.Add(RfcConfigParameters.Password, "yourpassword");
           conf.Add(RfcConfigParameters.Client, "001");
        }
        return conf;
     }
     
     public bool ChangeEventsSupported() {
        return true;
     }
     public event RfcDestinationManager.ConfigurationChangeHandler ConfigurationChanged;
}

You can refer below SAP link −

https://archive.sap.com/discussions/thread/3171324