Error displaying the categories

When I try to display the categories I get the following error message: Fatal error: Uncaught Error: Call to undefined function is_shop() in /www/htdocs/w0186f65/astrid-lindgren-schule-mh.de/wp-content/themes/higher-education-pro/inc/structure.php:121 Stack trace: #0 /www/htdocs/w0186f65/astrid-lindgren-schule-mh.de/wp-includes/class-wp-hook.php(286): higher_education_archive_header('') #1 /www/htdocs/w0186f65/astrid-lindgren-schule-mh.de/wp-includes/class-wp-hook.php(310): WP_Hook->apply_filters('', Array) #2 /www/htdocs/w0186f65/astrid-lindgren-schule-mh.de/wp-includes/plugin.php(453): WP_Hook->do_action(Array) #3 /www/htdocs/w0186f65/astrid-lindgren-schule-mh.de/wp-content/themes/higher-education-pro/header.php(86): do_action('higher_educatio...') #4 /www/htdocs/w0186f65/astrid-lindgren-schule-mh.de/wp-includes/template.php(688): require_once('/www/htdocs/w01...') #5 /www/htdocs/w0186f65/astrid-lindgren-schule-mh.de/wp-includes/template.php(647): load_template('/www/htdocs/w01...', true) #6 /www/htdocs/w0186f65/astrid-lindgren-schule-mh.de/wp-includes/general-template.php(41): locate_templ in /www/htdocs/w0186f65/astrid-lindgren-schule-mh.de/wp-content/themes/higher-education-pro/inc/structure.php on line 121 What can I do to fix it? Thank you for your help!