Have used Pressbooks before and all OK. Get this on fresh install:
Fatal error: Call to undefined function HM\Autoloader\register_class_path() in /home/admin/web/sitename.com/public_html/wp-content/plugins/pressbooks/pressbooks.php on line 77
“Copy Pressbooks’ autoloader file from /path/to/your/site/wp-content/plugins/pressbooks/hm-autoloader.php to /path/to/your/site/wp-content/mu-plugins/hm-autoloader.php. You may need to create the wp-content/mu-plugins/ directory if it doesn’t yet exist.”
I now get this after restarting server, if it helps:
Fatal error: Uncaught Error: Call to undefined function HM\Autoloader\register_class_path() in /home/admin/web/sitename.com/public_html/wp-content/plugins/pressbooks/pressbooks.php:77 Stack trace: #0 /home/admin/web/sitename.com/public_html/wp-admin/includes/plugin.php(1882): include() #1 /home/admin/web/sitename.com/public_html/wp-admin/plugins.php(164): plugin_sandbox_scrape(‘pressbooks/pres…’) #2 {main} thrown in /home/admin/web/sitename.com/public_html/wp-content/plugins/pressbooks/pressbooks.php on line 77