Fatal error: Uncaught TypeError: call_user_func_array(): Argument #1 ($callback) must be a valid callback, function "learn_press_course_comments_open" not found or invalid function name in /home/h286289/public_html/wp-includes/class-wp-hook.php:324 Stack trace: #0 /home/h286289/public_html/wp-includes/plugin.php(205): WP_Hook->apply_filters() #1 /home/h286289/public_html/wp-includes/comment-template.php(1317): apply_filters() #2 /home/h286289/public_html/wp-content/themes/iguru/learnpress/single-course.php(27): comments_open() #3 /home/h286289/public_html/wp-includes/template-loader.php(106): include('/home/h286289/p...') #4 /home/h286289/public_html/wp-blog-header.php(19): require_once('/home/h286289/p...') #5 /home/h286289/public_html/index.php(17): require('/home/h286289/p...') #6 {main} thrown in /home/h286289/public_html/wp-includes/class-wp-hook.php on line 324