How to get files from s3 and zip it before download

Question

I'm working on .net core web API and wanting to get the files from s3 and zip before download.
Can you point me to the right direction? I searched the web and couldn't find a solution.

so this block of code is able to read from s3 files (the bucket may contain different types of files), I just dont know how to zip all of them before download

public async Task GetFilesAsync(string projectId)        {
        string bucketName = "MyBucket";
        ListObjectsRequest request = new ListObjectsRequest
        {
            BucketName = bucketName
        };

        ListObjectsResponse response = await _client.ListObjectsAsync(request);
        var item = response.S3Objects;

        foreach (var objt in item)
        {
            GetObjectRequest request1 = new GetObjectRequest();
            request1.BucketName = bucketName;
            request1.Key = objt.Key;

            GetObjectResponse Response = await _client.GetObjectAsync(request1);

           //HOW TO ZIP all of the files here and download as single file
            using (Stream responseStream = Response.ResponseStream)
            {
               // Response.WriteResponseStreamToFile("downloadLocation" + "\\" + objt.Key);
            }

        }
}

I'm trying this solution but cannot make it work:

using (var compressedFileStream = new MemoryStream())
{
    //Create an archive and store the stream in memory.
    using (var zipArchive = new ZipArchive(compressedFileStream, ZipArchiveMode.Update, false))
    {
        foreach (var caseAttachmentModel in item)
        {
            //Create a zip entry for each attachment
            var zipEntry = zipArchive.CreateEntry(caseAttachmentModel.Key);

            //Get the stream of the attachment
            using (var originalFileStream = new MemoryStream(caseAttachmentModel.Body))
            using (var zipEntryStream = zipEntry.Open())
            {
                //Copy the attachment stream to the zip entry stream
                originalFileStream.CopyTo(zipEntryStream);
            }
        }

        return new FileContentResult(compressedFileStream.ToArray(), "application/zip") { FileDownloadName = "Filename.zip" };
    }
}