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 sql212.byetcluster.com. This could mean your host’s database server is down.
Are you sure you have the correct username and password?
Are you sure you have typed the correct hostname?
Are you sure the database server is running?
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.
The issue is that you have wrong info in the wp-config.php file. Your error says it was trying to accesss “sql212.byetcluster.com” but you are on “sql212.epizy.com”
“Error establishing a database connection” could mean anything. Could you please try enabling WP_DEBUG mode and refresh the page to get an actual error message?