ajax cross-domain request problem

The php side has header("Access-Control-Allow-Origin:*");

ajax request

<code>    $.ajax(
    {
        type : "post",
        url : url,
        async : false,
        dataType: 'json',
        data : {asdsa:1},
        success : function (obj)
        {
                //业务代码

        },
        error : function (obj) {
            alert('未找到文件');
        }
    }
    );</code>

If data is shorted, for example {}, an error will be reported. The CORS header is missing 'Access-Control-Allow-Origin'

Data Just write a parameter such as {dasdsa:1} and it's normal. What's going on?
This problem did not occur when cross-domain access was not bound to a domain name on the test machine, but now it does not work if the domain name is bound online

ps. There is a difference between testing and going online. Apache is used for testing the backend, and nginx is used for the backend going online. Does this have anything to do with it?