Upload json File to Zoho Docs with C# - "EMPTY_OR_NO_FILE_SPECIFIED"

Upload json File to Zoho Docs with C# - "EMPTY_OR_NO_FILE_SPECIFIED"

Hello,
For my business work, I'm trying to write a method in C# to upload json files to a contractor zoho docs account.
We have tried some different ways but with no success.
Connection is correctly established , if I insert a wrong token or folderId I got a bad request response.
But I didn't succeed to correctly insert the content of the file.
Always received response message  : "EMPTY_OR_NO_FILE_SPECIFIED"
Could someone help on this ?
Here is one of the test methods that return this response message : 
        public static void PostStockUnal(int sourceApiId)
        {
            string accessToken = "Zoho-oauthtoken " + token // generated with other method

            HttpContent content = new StringContent(stockReport, Encoding.UTF8, "application/json");
            Console.WriteLine("Start Request");

            HttpClient client = new HttpClient();
            client.DefaultRequestHeaders.Accept.Clear();
            client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("multipart/form-data"));
            client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", accessToken);

            Console.WriteLine("Content = " + content.Headers);

            var x = content.ReadAsStringAsync().Result;
            Console.WriteLine("Content = " + x);
            var resp = client.PostAsync("https://apidocs.zoho.com/files/v1/upload" + "?filename=Stock_snapshot20210210.json&fid=lz6x5c7bb900ad31343eeb9fe1a76c63d2a52"
                            , content).Result;
            Console.WriteLine("Resp Status Code= " + resp.StatusCode);
            Console.WriteLine("Res Read=" + resp.Content.ReadAsStringAsync().Result);
            Console.WriteLine(resp.ToString());
            if (resp.IsSuccessStatusCode)
            {
                JsonConvert.DeserializeObject<StockUploadResponse>(resp.Content.ReadAsStringAsync().Result);
            }
            Console.ReadLine();
        }






                          Zoho Desk Resources

                          • Desk Community Learning Series


                          • Digest


                          • Functions


                          • Meetups


                          • Kbase


                          • Resources


                          • Glossary


                          • Desk Marketplace


                          • MVP Corner


                          • Word of the Day



                              Zoho Marketing Automation



                                      Manage your brands on social media



                                              Zoho TeamInbox Resources

                                                Zoho DataPrep Resources



                                                  Zoho CRM Plus Resources

                                                    Zoho Books Resources


                                                      Zoho Subscriptions Resources

                                                        Zoho Projects Resources


                                                          Zoho Sprints Resources


                                                            Qntrl Resources


                                                              Zoho Creator Resources


                                                                Zoho WorkDrive Resources



                                                                  Zoho Campaigns Resources

                                                                    Zoho CRM Resources

                                                                    • CRM Community Learning Series

                                                                      CRM Community Learning Series


                                                                    • Tips

                                                                      Tips

                                                                    • Functions

                                                                      Functions

                                                                    • Meetups

                                                                      Meetups

                                                                    • Kbase

                                                                      Kbase

                                                                    • Resources

                                                                      Resources

                                                                    • Digest

                                                                      Digest

                                                                    • CRM Marketplace

                                                                      CRM Marketplace

                                                                    • MVP Corner

                                                                      MVP Corner


                                                                          Design. Discuss. Deliver.

                                                                          Create visually engaging stories with Zoho Show.

                                                                          Get Started Now