Such an error can occur in several cases:
There is no index file in the site directory. By default, it is a file named index.html, index.htm, index.php. If the index file is missing or unreadable, viewing the contents of the directory is blocked for security reasons. You can try adding an empty file called index.html and refresh the page to see if there is a problem.
Incorrect permissions for files and folders in the root directory of the site. On shared hosting, the correct permissions for files are 644, for folders - 755.
To enable viewing the contents of the directory without adding the index file, you can add in .htaccess parameter Options +Indexes a separate line at the beginning of the file.
Also, this error can occur due to the work of our security system on the hosting, namely if the data have been moved to quarantine by antivirus imunify360. In this case you should check the quarantine and add the moved files to the list of ignored items.
If these reasons are checked and the error is still present, please contact our technical support via ticket system.