试试这个PostAsJsonAsync

public ActionResult GetUserSchools(SchoolQueryModel getSchoolsModel)
{
    dynamic schoolDetails = null;

    using (var client = new HttpClient())
    {
        client.DefaultRequestHeaders.Add("Authorization", _infrastructureAuthKey);
        var responseTask = client.PostAsJsonAsync("http://localhost:6200/api/post_school_query", getSchoolsModel);
        if (responseTask.Result.IsSuccessStatusCode)
        {
            var readTask = responseTask.Result.Content.ReadAsAsync<JObject>();
            readTask.Wait();
            schoolDetails = readTask.Result;
        }
    }
}

这一条对我很有效，我还介绍了一些更好的做法：

• 利用async/await的功能。你不应该直接使用.Result。
• You should not create a HttpClient per request.

using System.Text;
using System.Text.Json;
using Microsoft.AspNetCore.Mvc;

namespace AspNetPlayground.Controllers;

[ApiController]
[Route("[controller]/[action]")]
public class TestController : ControllerBase
{
    private readonly HttpClient _httpClient;

    public TestController(IHttpClientFactory httpClientFactory) => _httpClient = httpClientFactory.CreateClient();

    [HttpPost]
    public Task<bool> IsNotNull([FromBody] SchoolQueryModel? schoolQueryModel) => Task.FromResult(schoolQueryModel is not null);

    [HttpPost]
    public async Task<bool> Run()
    {
        var getSchoolsModel = new SchoolQueryModel {SchoolIds = new() {Guid.NewGuid()}, DistrictIds = new() {Guid.NewGuid()}};
        using var requestContent = new StringContent(JsonSerializer.Serialize(getSchoolsModel), Encoding.UTF8, "application/json");
        using var response = await _httpClient.PostAsync("https://localhost:7041/Test/IsNotNull", requestContent);
        return response.IsSuccessStatusCode && await response.Content.ReadFromJsonAsync<bool>();
    }
}

public class SchoolQueryModel
{
    public List<Guid?> SchoolIds { get; init; } = new();
    public List<Guid?> DistrictIds { get; init; } = new();
}