There is an api service which can convert audio.wav file to text, and the text string would be returned as a field of json format. I tried to add new feature in a WinFrom program by C# .Net Framework to connect it to the API service to generate text files.
I used swagger and postman to test the API, and both of them successfully returned text generated from the audio file, but my WinFrom App always receives BadRequest 400.

I write a new ConsoleApp project to test the process of uploading a file to API and it also receives BadRequest 400. The errorContent show "TypeError: Cannot read properties of undefined (reading 'filename')n

 string url = "api endpoint";                    // API endpoint
 string filePath = "C:\test.wav";  // The path of audio file
 string token = "token";                  // The token to access the API endpoint
 string requestUri = $"xxx";

  using (var client = new HttpClient())
  {
      client.BaseAddress = new Uri(url);
     
      client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", token);

      using (var form = new MultipartFormDataContent())
      {
        
          byte[] fileBytes = File.ReadAllBytes(filePath);
          ByteArrayContent content = new ByteArrayContent(fileBytes);

          content.Headers.ContentType = new MediaTypeHeaderValue("audio/wav");
      
          form.Add(content, "audio", Path.GetFileName(filePath));

          var response = await client.PostAsync(requestUri, form);

          // Handle the response
          if (response.IsSuccessStatusCode)
          {
              var responseBody = await response.Content.ReadAsStringAsync();
              Console.WriteLine("Success: " + responseBody);
          }
          else
          {
              Console.WriteLine("Error: " + response.StatusCode);
              var errorContent = await response.Content.ReadAsStringAsync();
              Console.WriteLine("Error Details: " + errorContent);
          }
      }
  }

I tried to find the example code of uploading file by C# and ask ChatGPT to solve it, but I found their code are very similar with mine. The app still receive Bad Request 400 after I modify the code.