Absolute Beginners Group Class Level 2

Fatal error: Uncaught Error: Call to a member function get_stock_quantity() on bool in /home/customer/www/bangthedrumschool.com/public_html/wp-content/themes/epik/functions.php:416 Stack trace: #0 /home/customer/www/bangthedrumschool.com/public_html/wp-includes/shortcodes.php(355): show_qty_func(Array, '', 'show_qty') #1 [internal function]: do_shortcode_tag(Array) #2 /home/customer/www/bangthedrumschool.com/public_html/wp-includes/shortcodes.php(227): preg_replace_callback('/\\[(\\[?)(show_q...', 'do_shortcode_ta...', '<hr>\n<p><img da...') #3 /home/customer/www/bangthedrumschool.com/public_html/wp-includes/class-wp-hook.php(308): do_shortcode('<hr>\n<p><img da...') #4 /home/customer/www/bangthedrumschool.com/public_html/wp-includes/plugin.php(205): WP_Hook->apply_filters('<hr>\n<p><img da...', Array) #5 /home/customer/www/bangthedrumschool.com/public_html/wp-includes/post-template.php(255): apply_filters('the_content', '<hr>\r\n<img src=...') #6 /home/customer/www/bangthedrumschool.com/public_html/wp-content/themes/gene in /home/customer/www/bangthedrumschool.com/public_html/wp-content/themes/epik/functions.php on line 416