as the title suggests I get this error. (Notice: Undefined index: page in /Users/denis/Sites/www.testpepe.dev/wp-content/themes/bubi/functions.php on line 429)
Php code:

<?php
function bubi_ajax_script_load_more($args) {
    // Init ajax
    $ajax = false;
    // Call AJAX
    if(!empty($_SERVER['HTTP_X_REQUESTED_WITH']) &&
        strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) == 'xmlhttprequest') {
        $ajax = true;
        
        }
    //Number Paged
/* Line 429 */  $paged=$_POST['page'] + 1;
    // Number Article
    $num =4;
    //Args
    $args = array(
        'post_type' => 'post',
        'post_status' => 'publish',
        'posts_per_page' =>$num,
        'paged'=> $paged,
    );
        
        
    //Query
    $query = new WP_Query($args);
    if ($query->have_posts()):
        //loop articales
        while ($query->have_posts()): $query->the_post();
            //include articles template
            include 'template-parts/content-archive-design.php';
        endwhile;
    else:
        echo 0;
    endif;
    wp_reset_postdata();
    //Call AJAX
    if($ajax) die();

}

JS code:

<script>
jQuery.noConflict($);
/* Function AJAX */
jQuery(document).ready(function($) {

var eseguito = false;

//Scroll Position
$(window).scroll(function() {

    var $timeline_block = $('.cd-timeline-block');

    //hide timeline blocks which are outside the viewport
    $timeline_block.each(function(){
        if($(this).offset().top > $(window).scrollTop()+$(window).height()*0.75) {
            $(this).find('.cd-timeline-img, .cd-timeline-content').addClass('is-hidden');
        }
    });

    //on scolling, show/animate timeline blocks when enter the viewport
    $(window).on('scroll', function(){
        $timeline_block.each(function(){
            if( $(this).offset().top <= $(window).scrollTop()+$(window).height()*0.75 && $(this).find('.cd-timeline-img').hasClass('is-hidden') ) {
                $(this).find('.cd-timeline-img, .cd-timeline-content').removeClass('is-hidden').addClass('bounce-in');
            }
        });
    });
        
        //Init
        var that = $('#loadMore');
        var page = $('#loadMore').data('page');
        var newPage = page + 1;
        var ajaxurl = $('#loadMore').data('url');
        
    if (eseguito) {
        if ($(window).scrollTop() <= ($(document).height() - $(window).height())*0.75){
            eseguito = false;
        } else {
            return false;
        }
    }
        
    if (!eseguito) {
        
  
        if ($(window).scrollTop() >= ($(document).height() - $(window).height())*0.75){
            
    eseguito = true;
            
        //Call AJAX
        $.ajax({
            url: ajaxurl,
                type: 'post',
                data: {
                        page: page,
                        action: 'ajax_script_load_more'
                },
                error: function(response) {
                        console.log(response);
                },
                success: function(response) {
                        
                        if (response == 0) {
                    
                            if ($("#no-more").length == 0) {
                                $last =  ( 'placeholder', bubi_scripts_ajax_vars.placeholder_name);
                                    $('#ajax-content').append('<div id="no-more" class="text-center"><h3>'+$last+'</h3></div>');
                            }
                            $('.bubi_loader_ajax__dot').hide();
                        } else {
                            $('#loadMore').data('page', newPage);
                            $('#ajax-content').append(response);
                        }
                }
            });
        }
    }
    });
});
</script>

The code works fine, but in debug mode I get the error as per the title, how can I solve this problem? Thank you.