Ajax POST请求在允许源代码后不起作用

我有一个Ajax请求,如下所示:

$.ajax({
    url: "http://some-api.com/endpoint/",
    type: "POST",
    contentType: "application/json",
    headers: {
        'Access-Control-Allow-Origin': '*',
        'Content-Type': 'application/json'
    },
    data: '"data": "20200312',
    dataType: "json",
    success: function (data) {
        console.log(data);
    }
});

});

Access to XMLHttpRequest at 'http://some-api.com/endpoint/' from origin 'http://127.0.0.1:8000' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource

我做错了什么或错过了什么。我使用Django作为我的后端。它也可以在Postman中工作,但不能通过Ajax工作