zip a file programatically like native send to compressed zip folder

Question

I have to send a zipped file to an external application. Support on the other end says the application fails to read my programatically created file. This is how i create the file:

using System.IO;
using System.IO.Compression;

const string ZIPPATH = @".\stock.zip";
const string PACKAGEPATH = @".\stock\content";
const string APPPACKAGE = @".\stock";
const string PACKAGEFILENAME = @"content\Offers.xml";

private void CreateZipArchive()
{
    if (!Directory.Exists(PACKAGEPATH)) Directory.CreateDirectory(PACKAGEPATH);

    if (File.Exists(ZIPPATH)) File.Delete(ZIPPATH);

    ZipFile.CreateFromDirectory(APPPACKAGE, ZIPPATH);
    using (FileStream fs = new FileStream(ZIPPATH, FileMode.Open))
    using (ZipArchive archive = new ZipArchive(fs, ZipArchiveMode.Update))
    {
        ZipArchiveEntry zae = archive.CreateEntry(PACKAGEFILENAME);
        using (StreamWriter sw = new StreamWriter(zae.Open(), new UTF8Encoding(true)))
        {
           // xml writing code ...
            sw.Write("--snipped--");
        }
    }
}

the folder APPPACKAGE contains some required files. After zip creation I insert my created xml file. inspecting the contents of the created zip file everything looks right yet the recipient application fails to read it. My question is: Is there something I might have missed?

Edit: Client gave me little additional Feedback. The only thing mentioned was that filure to read the package can happen if there is an md5 error. I suspect now that it could be related to the order in which I create the package. I'll try to first create the xml file and then create the zip file

Answer 1

Although LukaszSzczygielek pointed out another possible Issue in zip file creation the solution of my particular problem is to first create the files and then create the package:

using System.IO;
using System.IO.Compression;

const string ZIPPATH = @".\stock.zip";
const string PACKAGEPATH = @".\stock\content";
const string APPPACKAGE = @".\stock";
const string PACKAGEFILENAME = @"\Offers.xml";

private void CreateZipArchive()
{
    if (!Directory.Exists(PACKAGEPATH)) Directory.CreateDirectory(PACKAGEPATH);

    if (File.Exists(ZIPPATH)) File.Delete(ZIPPATH);

    string fileFullPath = PACKAGEPATH + PACKAGEFILENAME;
    using(Stream fs = new FileStream(fileFullPath, FileMode.Create, FileAccess.Write))
    using(StreamWriter sw = new StreamWriter(fs, new UTF8Encoding(true)))
    {
        // xml writing code ...
        sw.Write("--snipped--");
    }

    ZipFile.CreateFromDirectory(APPPACKAGE, ZIPPATH);
}