Hi Osama Alajarmeh ,  instead of providing a source folder, you should provide the data bytes of the file/s you are communicating to the API endpoint.  The following is an example of how you might go about this.

        // Replace these values with actual values
        string baseUrl = "https://example.com/api/projectserver/v2/";
        string projectId = "yourProjectId";
        string languageFileId = "yourLanguageFileId";
        string filePath = "path_to_your_file.txt"; // Path to the file you want to upload

        using (var httpClient = new HttpClient())
        {
            // Prepare the request URL
            string apiUrl = $"projects/{projectId}/files/{languageFileId}/upload";
            string requestUrl = new Uri(new Uri(baseUrl), apiUrl).ToString();

            // Read the file into a byte array
            byte[] fileBytes = File.ReadAllBytes(filePath);

            // Create the content for the HTTP request
            using (var content = new MultipartFormDataContent())
            {
                content.Add(new ByteArrayContent(fileBytes), "file", Path.GetFileName(filePath));

                // Send the POST request
                HttpResponseMessage response = await httpClient.PostAsync(requestUrl, content);

                // Process the response
                if (response.IsSuccessStatusCode)
                {
                    Console.WriteLine("File uploaded successfully.");
                }
                else
                {
                    Console.WriteLine($"File upload failed. Status code: {response.StatusCode}");
                }
            }
        }

let me know how it goes,

Hi Patrick Andrew Hartnett 

Thank you so much for this solution!