在函数的入口处添加以下代码解决该问题。

using System.Net;
using Newtonsoft.Json;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Primitives;

public static async Task Run(HttpRequest req, ILogger log)
{
    var settings = new JsonSerializerSettings
    {
        ReferenceLoopHandling = ReferenceLoopHandling.Ignore
    };
    var requestBody = await new StreamReader(req.Body).ReadToEndAsync();
    dynamic data = JsonConvert.DeserializeObject(requestBody, settings);
    // function code logic here

    return (ActionResult)new OkObjectResult($"Hello, {data.name}");
}

以上代码操作序列化和反序列化的Json.NET，将ReferenceLoopHandling设置为Ignore。这将忽略循环引用。