Fatal error: Uncaught TypeError: call_user_func_array(): Argument #1 ($callback) must be a valid callback, function "storefront_upsell_display" not found or invalid function name in /bermaxks/www/html/wp-includes/class-wp-hook.php:324 Stack trace: #0 /bermaxks/www/html/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters('', Array) #1 /bermaxks/www/html/wp-includes/plugin.php(517): WP_Hook->do_action(Array) #2 /bermaxks/www/html/wp-content/themes/child-theme/woocommerce/single-product.php(69): do_action('woocommerce_aft...') #3 /bermaxks/www/html/wp-includes/template-loader.php(106): include('/bermaxks/www/h...') #4 /bermaxks/www/html/wp-blog-header.php(19): require_once('/bermaxks/www/h...') #5 /bermaxks/www/html/index.php(17): require('/bermaxks/www/h...') #6 {main} thrown in /bermaxks/www/html/wp-includes/class-wp-hook.php on line 324