Php AJAX请求创建thumbail created 503错误

我有一个文件夹中的图像，我需要转换成缩略图使用PHP。我写了两个代码，但每个都有自己的问题

例1-使用此代码，我无法获得返回浏览器的响应，因此我可以更新进度条

$('#id_xyz').click(function() {
    $.ajaxSetup({
        headers: {
            'X-CSRF-TOKEN': $('#id_xyz').attr('data-csrf')
        }
    });
    $url = $(this).attr('data-url');
    $('.success-message').css('display', 'block');
    $.ajax({
        type: "GET",
        url: $url,
        dataType: "json",
        async: false,
        data: {file_name: 'count'},
        success: function(data) {
            $('#progress-bar').attr('max', data.length);
            $('#total_files').html(data.length);
            $total_count = data.length;
            $count = 1;
            $(data).each(function(index) {
                $.ajax({
                    type: "GET",
                    url: $url,
                    async: false,
                    tryCount: 0,
                    retryLimit: 3,
                    data: {file_name: this},
                    success: function(data) {  
                        $('#progress-bar').val($count++);                        
                        $('#current-file').html($count); 
                    },
                    error: function(xhr, textStatus, errorThrown) {

                    }

                }, "json");
            });

        },
        beforeSend: function(data) {
        }
    }, "json");
});

---

例2-使用这个，我在发送了几个请求后收到503服务器错误

$('#id_xyz').click(function() {
    $.ajaxSetup({
        headers: {
            'X-CSRF-TOKEN': $('#id_xyz').attr('data-csrf')
        }
    });
    $url = $(this).attr('data-url');
    $('.success-message').css('display', 'block');
    $.ajax({
        type: "GET",
        url: $url,
        dataType: "json",
        async: false,
        data: {file_name: 'count'},
        success: function(data) {
            $('#progress-bar').attr('max', data.length);
            $('#total_files').html(data.length);
            $total_count = data.length;
            $count = 1;
            $(data).each(function(index) {
                $.ajax({
                    type: "GET",
                    url: $url,
                    async: true,
                    tryCount: 0,
                    retryLimit: 3,
                    data: {file_name: this},
                    success: function(data) {  
                        $('#progress-bar').val($count++);                        
                        $('#current-file').html($count); 
                    },
                    error: function(xhr, textStatus, errorThrown) {

                    }

                }, "json");
            });

        },
        beforeSend: function(data) {
        }
    }, "json");
});

请帮我解决这个问题