试图在java spring中调用发布第三方api

我的问题是，当我try 这一点时，我得到了一个媒体类型错误，然后我更改了标题.现在我收到一个500错误.问题不在于api，它在postman上运行得很好，我在请求帖子时是否在代码中出错？

我的对象模型

private String module;
    private String notificationGroupType;
    private String notificationGroupCode;
    private String notificationType;
    private String inLineRecipients;
    private String eventCode;
    private HashMap<String, Object> metaData;

    public EmailModel() {
        this.module = "CORE";
        this.notificationGroupType ="PORTAL";
        this.notificationGroupCode = "DEFAULT";
        this.notificationType =  "EMAIL";
        this.inLineRecipients ="[chrispotjnr@gmail.com,chris@mqattach.com]";
        this.eventCode = "DEFAULT";
        this.metaData = metaData;
    }
 

我的控制器

 private EmailModel em;
    @RequestMapping(value = "test", method = RequestMethod.Post)
    public void post() throws Exception {
        String uri= "TestUrl";


        EmailModel em = new EmailModel();
                EmailModel data =em;

        HttpClient client = HttpClient.newBuilder().build();
        HttpRequest request = HttpRequest.newBuilder()
                .headers("Content-Type", "application/json")
                .uri(URI.create(uri))
                .POST(HttpRequest.BodyPublishers.ofString(String.valueOf(data)))
                .build();

        HttpResponse<?> response = client.send(request, HttpResponse.BodyHandlers.discarding());
        System.out.println(em);
        System.out.println(response.statusCode());

    }

postmanImage