This either means that the username and password information in your
wp-config.php file is incorrect or we can’t contact the database server at
main-san-db-instance.chfhobetlx68.us-east-2.rds.amazonaws.com. This could mean your host’s database server is down.
If you’re unsure what these terms mean you should probably contact your host. If you still need help you can always visit the WordPress Support Forums.