Saving and displaying Custom Post Type metadata

Hi Everyone,

I’m having trouble saving and using metadata from a custom post type. When I update the post, the field shows up blank. I’d like this metadata to be saved and used as a link on the front page.

Here’s my custom post type file, which includes the code for adding the meta box and saving it:

<?php
/**
 * @package Hot_Stuff
 */
/*
Plugin Name: Hot Stuff
Description: Enter and present hot products
Author: Backstage Interactive
Author URI: https://backstageinteractive.com
Version: 1.0
Text Domain: hotstuff
*/

// Register Custom Post Type
function hot_stuff_post_type() {

	$labels = array(
		'name'                  => _x( 'Products', 'Post Type General Name', 'hotstuff' ),
		'singular_name'         => _x( 'Product', 'Post Type Singular Name', 'hotstuff' ),
		'menu_name'             => __( 'Hot Stuff Products', 'hotstuff' ),
		'name_admin_bar'        => __( 'Hot Stuff', 'hotstuff' ),
		'archives'              => __( 'Product Archives', 'hotstuff' ),
		'attributes'            => __( 'Product Attributes', 'hotstuff' ),
		'parent_item_colon'     => __( 'Parent Product:', 'hotstuff' ),
		'all_items'             => __( 'All Products', 'hotstuff' ),
		'add_new_item'          => __( 'Add New Product', 'hotstuff' ),
		'add_new'               => __( 'Add New', 'hotstuff' ),
		'new_item'              => __( 'New Product', 'hotstuff' ),
		'edit_item'             => __( 'Edit Product', 'hotstuff' ),
		'update_item'           => __( 'Update Product', 'hotstuff' ),
		'view_item'             => __( 'View Product', 'hotstuff' ),
		'view_items'            => __( 'View Products', 'hotstuff' ),
		'search_items'          => __( 'Search Product', 'hotstuff' ),
		'not_found'             => __( 'Not found', 'hotstuff' ),
		'not_found_in_trash'    => __( 'Not found in Trash', 'hotstuff' ),
		'featured_image'        => __( 'Product Image', 'hotstuff' ),
		'set_featured_image'    => __( 'Set Product image', 'hotstuff' ),
		'remove_featured_image' => __( 'Remove Product image', 'hotstuff' ),
		'use_featured_image'    => __( 'Use as Product image', 'hotstuff' ),
		'insert_into_item'      => __( 'Insert into Product', 'hotstuff' ),
		'uploaded_to_this_item' => __( 'Uploaded to this Product', 'hotstuff' ),
		'items_list'            => __( 'Products list', 'hotstuff' ),
		'items_list_navigation' => __( 'Products list navigation', 'hotstuff' ),
		'filter_items_list'     => __( 'Filter Products list', 'hotstuff' ),
	);
	$rewrite = array(
		'slug'                  => 'stuff',
		'with_front'            => false,
		'pages'                 => false,
		'feeds'                 => false,
	);
	$args = array(
		'label'                 => __( 'Product', 'hotstuff' ),
		'description'           => __( 'Add stuff to GiveMeStuff', 'hotstuff' ),
		'labels'                => $labels,
		'supports'              => array( 'title', 'editor', 'excerpt', 'author', 'thumbnail', 'comments', 'trackbacks', 'revisions', 'custom-fields', 'post-formats', ),
		'taxonomies'            => array( 'product_type', '' ),
		'hierarchical'          => false,
		'public'                => true,
		'show_ui'               => true,
		'show_in_menu'          => true,
		'menu_position'         => 5,
		'menu_icon'             => 'dashicons-cart',
		'show_in_admin_bar'     => true,
		'show_in_nav_menus'     => true,
		'can_export'            => true,
		'has_archive'           => true,		
		'exclude_from_search'   => false,
		'publicly_queryable'    => true,
		'rewrite'               => $rewrite,
		'capability_type'       => 'page',
		'show_in_rest'          => true,
	);
	register_post_type( 'hot_stuff', $args );

}
add_action( 'init', 'hot_stuff_post_type', 0 );

/* Fire our meta box setup function on the post editor screen. */
add_action( 'load-post.php', 'hotstuff_post_meta_boxes_setup' );
add_action( 'load-post-new.php', 'hotstuff_post_meta_boxes_setup' );

/* Meta box setup function. */
function hotstuff_post_meta_boxes_setup() {

  /* Add meta boxes on the 'add_meta_boxes' hook. */
  add_action( 'add_meta_boxes', 'hotstuff_add_post_meta_boxes' );

  /* Save post meta on the 'save_post' hook. */
  add_action( 'save_post', 'hotstuff_save_link_meta', 10, 2 );

}

/* Create one or more meta boxes to be displayed on the post editor screen. */
function hotstuff_add_post_meta_boxes() {

	add_meta_box(
    	'hotstuff-link',      // Unique ID
    	esc_html__( 'Gimme Button Link', 'example'),    // Title
    	'hotstuff_link_meta_box',   // Callback function
    	'hot_stuff',         // Admin page (or post type)
    	'advanced',         // Context
    	'default'         // Priority
    );
}

/* Display the Link post meta box. */
function hotstuff_link_meta_box( $post ) { ?>

  <?php wp_nonce_field( basename( __FILE__ ), 'hotstuff_link_nonce' ); ?>

  <p>
    <label for="hotstuff-link"><?php _e( "Enter affiliate link", 'example' ); ?></label>
    <br />
    <input class="widefat" type="text" name="hotstuff-link" id="hotstuff-link" value="<?php echo esc_attr( get_post_meta( $post->ID, 'hotstuff_link', true ) ); ?>" size="30" />
  </p>
<?php }

/* Save the meta box's post metadata. */
function hotstuff_save_link_meta( $post_id, $post ) {

  /* Verify the nonce before proceeding. */
  if ( !isset( $_POST['hotstuff_link_nonce'] ) || !wp_verify_nonce( $_POST['hotstuff_link_nonce'], basename( __FILE__ ) ) )
    return $post_id;

  /* Get the post type object. */
  $post_type = get_post_type_object( $post->post_type );

  /* Check if the current user has permission to edit the post. */
  if ( !current_user_can( $post_type->cap->edit_post, $post_id ) )
    return $post_id;

  /* Get the meta key. */
  $meta_key = 'hotstuff_link';

  /* Get the meta value of the custom field key. */
  $meta_value = get_post_meta( $post_id, $meta_key, true );

  /* If a new meta value was added and there was no previous value, add it. */
  if ( $new_meta_value && '' == $meta_value )
    add_post_meta( $post_id, $meta_key, $new_meta_value, true );

  /* If the new meta value does not match the old value, update it. */
  elseif ( $new_meta_value && $new_meta_value != $meta_value )
    update_post_meta( $post_id, $meta_key, $new_meta_value );

  /* If there is no new meta value but an old value exists, delete it. */
  elseif ( '' == $new_meta_value && $meta_value )
    delete_post_meta( $post_id, $meta_key, $meta_value );
}

add_filter( 'template_include', 'include_template_function', 1 );

function single_product_template( $template_path ) {
    if ( get_post_type() == 'hot_stuff' ) {
        if ( is_single() ) {
            // checks if the file exists in the theme first,
            // otherwise serve the file from the plugin
            if ( $theme_file = locate_template( array ( 'single-product.php' ) ) ) {
                $template_path = $theme_file;
            } else {
                $template_path = plugin_dir_path( __FILE__ ) . '/single-product.php';
            }
        }
    }
    return $template_path;
}

function product_remove_cpt_slug( $post_link, $post, $leavename ) {
 
    if ( 'hot_stuff' != $post->post_type || 'publish' != $post->post_status ) {
        return $post_link;
    }
 
    $post_link = str_replace( '/' . $post->post_type . '/', '/', $post_link );
 
    return $post_link;
}
add_filter( 'post_type_link', 'product_remove_cpt_slug', 10, 3 );

function product_parse_request_trick( $query ) {
 
    // Only noop the main query
    if ( ! $query->is_main_query() )
        return;
 
    // Only noop our very specific rewrite rule match
    if ( 2 != count( $query->query ) || ! isset( $query->query['page'] ) ) {
        return;
    }
 
    // 'name' will be set if post permalinks are just post_name, otherwise the page rule will match
    if ( ! empty( $query->query['name'] ) ) {
        $query->set( 'post_type', array( 'post', 'page', 'hot_stuff' ) );
    }
}
add_action( 'pre_get_posts', 'product_parse_request_trick' );

Here’s the code from my content file. The idea is to use the url that gets entered in the meta box as a link:

<a href="<?php echo $hotstuff_link; ?>" class="gimme-button">Gimme</a>

Any help would be greatly appreciated.