The WordPress Ajax request returns 0

I can’t figure out why nothing is returned
I am a real beginner in Ajax ..
I just read a lot of topics about using Ajax in Woprdpress but the examples are super advanced for me
Here is my JS code combo_checkout_iRange.js

jQuery(document).ready(function() {
    jQuery('#loader').hide();
    jQuery('#check-out-date').hide();
    jQuery('#check-in-date').change(function(){
        jQuery('#check-out-date').fadeOut();
        jQuery('#loader').show();
        jQuery.ajax({
            type: 'POST',
            url:myAjax.ajaxurl, 
            data: {
                action : 'my_ajax_handler',
                parent_id: jQuery("#check-in-date").val()
            },
            success: function(data){
                alert(data);
                jQuery('#loader').hide();
                jQuery('#check-out-date').show();
                jQuery('#check-out-date').append(data);
            }});
            return false;
        });
        jQuery('#check-out-date').change(function(){
            alert(jQuery('#check-out-date').val());
        });
    });

This is what I wrote on function.php

Note: this should work in post type called “meetings”

add_action("wp_enqueue_scripts", function() {

     if (is_single()) {
        if (get_post_type() == 'meetings')
        {
            wp_enqueue_script('combo_checkout_iRange', get_template_directory_uri() . '/js/combo_checkout_iRange.js', array( 'jquery' ), '1.0' ,true);

            $data_array = array(
                'ajaxurl' => admin_url( 'admin-ajax.php' )
            );

            wp_register_script( 'combo_checkout_iRange', get_template_directory_uri() . '/js/combo_checkout_iRange.js', array('jquery') );
            wp_localize_script( 'combo_checkout_iRange', 'myAjax', $data_array );



        }
    }
});

and this is my ajax handler i put it inside single_meetings.php

add_action("wp_ajax_my_ajax_handler", "my_ajax_handler");
add_action("wp_ajax_nopriv_my_ajax_handler", "my_ajax_handler");

function my_ajax_handler() {
                if ( isset($_REQUEST["parent_id"]) ) {
                     $id    = $_REQUEST["parent_id"];
                     return $id;
                     die();
                 }
             }