C#.NET Core 3.1 Web API Post参数为Null

我试图使用以下代码从WPF向Web API发出post请求，但请求参数始终为空。

请求模型

public class Document
{
   public string FileName { get; set; }
   public byte[] Buffer { get; set; }
}


public class Request
{
   public string Uploader { get; set; }
   public List<Document> Documents { get; set; }
}

WPF客户端

var obj = new Request()
{
    Uploader = "John Doe",
    Documents = new List<Document>
    {
        new Document()
        {
            FileName ="I Love Coding.pdf",
            Buffer = System.IO.File.ReadAllBytes(@"C:\Users\john.doe\Downloads\I Love Coding.pdf.pdf")
        }
    }
};

using (var http = new HttpClient())
{
    var encodedJson = JsonConvert.SerializeObject(obj);
    var conent = new StringContent(encodedJson, Encoding.UTF8, "application/json");
    HttpResponseMessage response = await http.PostAsync("https://my-app.com/api/upload", conent);
    response.EnsureSuccessStatusCode();
}

Web API

[Route("")]
public class AppController : ControllerBase
{
    [HttpPost]
    [Route("api/upload")]
    public async Task<IActionResult> UploadDocumentsAsync([FromBody] Request request)
    {
        // request is always null when app is running in production
        // https://my-app.com/api/upload

        //request is not null when running on https://localhost:8080/api/upload
    }
}

请问我在上述实施中缺少什么？请求参数在本地主机上不为空，但在生产中始终为空。