The list of paths to trusted SSH key files controls the public / private key authentication that SFTP allows for.  This setting does not want you to enter in a 'trusted keys file', or a folder path, but rather the path to the actual key file itself.  So '/files/keys/' is bad, while '/files/keys/' would be OK.  Separate multiple items with new lines.  Most SSH key formats are supported.


There is also a more generic way to use this field.  If the key file has the exact name of the user logging in, you can instead reference the directory '/files/keys/'.  In this case there would need to be a file named 'ben' in that directory.