A database connection could not be established. Error

Error » Main

Message Class 'fSession' not found
File /var/www/vhosts/wowcanisee.com/httpdocs/src/Core/Setup/Session.php
Line 18
Date Sun, 23 Feb 2020 23:53:22 +1000
URL http://wowcanisee.com/
Referring URL (Unknown)
Request Method GET
User-agent CCBot/2.0 (https://commoncrawl.org/faq/)
PHP error Use of undefined constant DEVELOPMENT_MODE - assumed 'DEVELOPMENT_MODE'

Error » Trace

File /var/www/vhosts/wowcanisee.com/httpdocs/src/Core/Bootstrap.php
Line 35
Class Setup_Session
Function setup
File /var/www/vhosts/wowcanisee.com/httpdocs/index.php
Line 64
Class Bootstrap
Function init