If you see the following error :-
DATABASE ERROR: CONNECTION FAILED!
Unable to connect to the database!
Please contact your server-administrator.
You can run the folowing script to solve the issue
/scripts/upcp --force to update cPanel
You can also run the following command to solve the issue
Login details in the /usr/local/cpanel/base/roundcube/config/db.inc.php file and check
since it's clear the DB connection error.
root@test [/usr/local/cpanel/base/roundcube]# cat config/db.inc.php | grep roundcube
$rcmail_config['db_dsnw'] = 'mysql://roundcube:DB_PASSWORDlocalhost/roundcube';
// postgres example: 'pgsql://roundcube:pass@localhost/roundcubemail';
PS: Roundcube database Name: roundcube
DB Roundcube Database username : roundcube
DB password : DB_PASSWORD //it has in /root/.my.cnf file