C#-Indice.EDI define FTX segment

Question

I have to change a module that another developer has created. No documentation whatsoever available... Now my customer wants to add an FTX segment, I can define an FTX-element with all the necessary information, but after I add it to the envelope the data fields are empty.

var grammar = EdiGrammar.NewTradacoms();
            grammar.SetAdvice(
                                         segmentNameDelimiter: '+',
                                         dataElementSeparator: '+',
                                         componentDataElementSeparator: ':',
                                         segmentTerminator: '\'',
                                         releaseCharacter: null,
                                         reserved: null,
                                         decimalMark: '.');

            var interchange = new order_edi();

FTX dummy= new DataBase.EDIFact.FTX();
...
d.Fieldummy1 = order.desc.Substring(0, 70);
...
interchange.free_text.Append(dummy);
...
using (var textWriter = new StreamWriter(File.Open(file.Replace("pdf", "edi"), FileMode.Create)))
                {
                    using (var ediWriter = new EdiTextWriter(textWriter, grammar))
                    {
                        new EdiSerializer().Serialize(ediWriter, interchange);
                    }
                }

And heres the code snippet from order_edi

public FTX[] free_text { get; set; }

Has anyone a working example based on Indice.EDI? Or some tipps/hints? I don't really want to rewrite the whole interface.

Thanx in advance.