Why am I receiving phpBB: Critical Error Could not connect to the database error?
This error most probably means that you have not configured your phpBB’s database settings properly. Check phpBB’s configuration file config.php located in the directory where your forum resides. To edit the file, use your File Manager in Site Tools.
Another reason for this error is when your database has been deleted. In this case, it would be best to restore it from a backup.
If you have problems with your phpBB forum, ask your host for assistance.