How to call update_post_meta?

I have a custom script for updating a custom post type. The calling script passes the post id of the post meta and populates a web page. The purpose of the page is to allow the user to update existing post meta data. The display aspect of the script works fine.?

I started using ajax for the update function. My problem is the code returns a success message yet nothing is actually updated. I do not know how to debug this. 

Can you point out the flaws or omissions in my code?

Thank you!

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Here is my code in that calls the update function 

   $(‘#update-time-entry’).click(function(event) {

    var user_id = jQuery(‘#user_id’).val();

    var user_name = jQuery(‘#user_name’).val();

    var start_time = jQuery(‘#start_time’).val();

    var end_time = jQuery(‘#end_time’).val();

    var project_title = jQuery(‘#project-select’).val();

    var project_description = jQuery(‘#project_desc’).val();

    var payroll = jQuery(‘#payroll-select’).val();

Select allOpen in new window

    var update_time_entry = new FormData();

    update_time_entry.append(‘action’, ‘update_time_entry’);

    update_time_entry.append(‘update_post_id’, update_post_id);

    update_time_entry.append(‘user_id’, user_id);

    update_time_entry.append(‘user_name’, user_name);

    update_time_entry.append(‘start_time’, start_time);

    update_time_entry.append(‘end_time’, end_time);

    update_time_entry.append(‘project_title’, project_title);

    update_time_entry.append(‘project_description’, project_description);

    update_time_entry.append(‘payroll’, payroll);

    jQuery.ajax({

        type: “post”,

        dataType: “json”,

        url: “<?php echo admin_url(‘admin-ajax.php’); ?>”,

        cache: false,

        processData: false,

        contentType: false,

        enctype: ‘multipart/form-data’,

        data: update_time_entry,

        success: function(data) {

            if (data.id == ‘success’) {

Here is the update function code 

function update_time_entry() {

    $update_post_id = sanitize_text_field($_POST[‘update_post_id’]);

    $action = sanitize_text_field($_POST[‘action’]);

    $user_id = sanitize_text_field($_POST[‘user_id’]);

    $user_name = sanitize_text_field($_POST[‘user_name’]);

    $start_time = sanitize_text_field($_POST[‘start_time’]);

    $end_time = sanitize_text_field($_POST[‘end_time’]);

    $project_title = sanitize_text_field($_POST[‘project_title’]);

    $payroll = sanitize_text_field($_POST[‘payroll’]);

    $project_description = sanitize_text_field($_POST[‘project_description’]);

    // =============================CODE MODIFICATION========================

    update_post_meta($update_post_id, ‘action’, $action);

    update_post_meta($update_post_id, ‘user_id’, $user_id);

    update_post_meta($update_post_id, ‘user_name’, $user_name);

    update_post_meta($update_post_id, ‘start_time’, $start_time);

    update_post_meta($update_post_id, ‘end_time’, $end_time);

    update_post_meta($update_post_id, ‘project_title’, $project_title);

    update_post_meta($update_post_id, ‘project_description’, $project_description);

    update_post_meta($update_post_id, ‘payroll’, $payroll);

    // =============================CODE MODIFICATION================================

    echo json_encode(array(‘id’ => ‘success’));

    exit();

}