“Unable to connect to backend”

Plugin version 2.2
WordPress version 4.9.6
PHP version 7.2

When I install and activate the plugin I get the error “Unable to connect to backend”. The error logs show the following 2 errors.

A PHP Warning:

PHP Warning:  Use of undefined constant CYSTEME_FINDER - assumed 'CYSTEME_FINDER' (this will throw an Error in a future version of PHP) in /home/PATH_TO_WP/wp-content/plugins/cysteme-finder/cysteme-finder.php on line 13

A PHP Fatal Error:

PHP Fatal error:  Uncaught ArgumentCountError: Too few arguments to function cysteme_finder_connector(), 0 passed in /home/PATH_TO_WP/wp-content/plugins/cysteme-finder/cysteme-finder.php on line 157 and exactly 1 expected in /home/PATH_TO_WP/wp-content/plugins/cysteme-finder/cysteme-finder.php:123
Stack trace:
#0 /home/PATH_TO_WP/wp-content/plugins/cysteme-finder/cysteme-finder.php(157): cysteme_finder_connector()
#1 /home/PATH_TO_WP/wp-settings.php(305): include_once('/home/ipsthete/...')
#2 /home/PATH_TO_WP/wp-config.php(89): require_once('/home/ipsthete/...')
#3 /home/PATH_TO_WP/wp-load.php(37): require_once('/home/ipsthete/...')
#4 /home/PATH_TO_WP/wp-admin/admin.php(31): require_once('/home/ipsthete/...')
#5 /home/PATH_TO_WP/wp-admin/options-general.php(10): require_once('/home/... in /home/PATH_TO_WP/wp-content/plugins/cysteme-finder/cysteme-finder.php on line 123