add_action( 'add_meta_boxes', 'rt_book_sales' );
add_action( 'wp_ajax_rt_book_name_rander', 'rt_book_name_rander' );
add_action( 'save_post', 'rt_book_name_rander', 10, 3 );
function rt_book_sales(){
add_meta_box( 'rt_bk_goal', 'Meta Box Title', 'rt_books_meta_rander', 'post', 'normal', 'high' );
}
function rt_books_meta_rander(){
?>
</div class= "wrap">
   <input  type="text" name="book_name" id="book_name" >
   <input  type="submit" class="rt_bk_btn">
</div>
<?php
}
?>

$(document).on('click', '.rt_bk_btn', function(e) {
e.preventDefault();
var bk_name = $('#book_name').val();

var data = {
'bk_name': bk_name,
'action': 'rt_book_name_rander',
}
$.post(ajaxurl, data, function(resp){
console.log(resp);
});

function rt_book_name_rander(){
global $post;

if (isset($_POST['bk_name'])) {
        $bk_name = $_POST['bk_name'];
        update_post_meta( $post->ID, 'rt_book', $bk_name );
    }

    die(0);
}

add_action( 'add_meta_boxes', 'rt_book_sales' );
add_action( 'wp_ajax_rt_book_name_rander', 'rt_book_name_rander' );
function rt_book_sales(){
    add_meta_box( 'rt_bk_goal', 'Meta Box Title', 'rt_books_meta_rander', 'post', 'normal', 'high' );
}

function rt_books_meta_rander($post){
?>
</div class= "wrap">
   <input type="text" name="book_name" id="book_name" value="<?php echo esc_attr(get_post_meta( $post->ID, 'rt_book', true )); ?>">
   <input type="submit" class="rt_bk_btn">
</div>
<?php
}

add_action('admin_footer', 'my_admin_add_js');
function my_admin_add_js() {
    ?>
    <script>
        jQuery(document).ready(function($) {
            $(document).on('click', '.rt_bk_btn', function(e) {
                e.preventDefault();
                var bk_name = $('#book_name').val();
                var post_id = $('input[name="post_ID"]').val();
                var data = {
                    'post_id': post_id,
                    'bk_name': bk_name,
                    'action': 'rt_book_name_rander',
                }
                $.post(ajaxurl, data, function(resp){
                    console.log(resp);
                });
            });
        });
    </script>
    <?php
}

function rt_book_name_rander(){
    if (isset($_POST['bk_name']) && isset($_POST['post_id'])) {
        $bk_name = $_POST['bk_name'];
        update_post_meta( $_POST['post_id'], 'rt_book', $bk_name );
    }

    die();
}