I am running WordPress 5.9.5. This is a fresh install of WordPress.
When attempting to activate the plugin 'Realty Portal: Agent' version 0.3.9 I get the following error:
Fatal error: Uncaught Error: Undefined constant "REALTY_PORTAL" in /homepages/12/d936913757/htdocs/clickandbuilds/GottaGoGirl/wp-content/plugins/realty-portal-agent/realty-portal-agent.php:179 Stack trace: #0 /homepages/12/d936913757/htdocs/clickandbuilds/GottaGoGirl/wp-includes/class-wp-hook.php(307): RP_AddOn_Agent::activation('') #1 /homepages/12/d936913757/htdocs/clickandbuilds/GottaGoGirl/wp-includes/class-wp-hook.php(331): WP_Hook->apply_filters('', Array) #2 /homepages/12/d936913757/htdocs/clickandbuilds/GottaGoGirl/wp-includes/plugin.php(474): WP_Hook->do_action(Array) #3 /homepages/12/d936913757/htdocs/clickandbuilds/GottaGoGirl/wp-admin/plugins.php(194): do_action('activate_realty...') #4 {main} thrown in /homepages/12/d936913757/htdocs/clickandbuilds/GottaGoGirl/wp-content/plugins/realty-portal-agent/realty-portal-agent.php on line 179
All other plugins activate with zero errors.