I am encountering the error file_folder_err_invalid because the path / is being passed. If I add the parameter prefix /, uploading to the root works, but everything else fails. The issue seems to be related to DIRECTORY_SEPARATOR on Windows, as DIRECTORY_SEPARATOR does not match $container. This discrepancy is likely causing the problem.
MODX 3.0.5
php7.4
WINDOWS DIRECTORY_SEPARATOR = \