The author of the plugin is here.
The fields.dir attribute fields.dir not indicate what the subdirectory should be. This is a link to a column in your database table where we have to save director , where we saved the file.
If you want to change the location where files are saved on disk, you should use the path option instead. Here is an example when I use the photo_dir subdirectory:
$this->addBehavior('Josegonzalez/Upload.Upload', [ 'avatar' => [ 'path' => 'webroot{DS}files{DS}{model}{DS}{field}{DS}photo_dir{DS}' ] ]);
The default value for the path parameter is webroot{DS}files{DS}{model}{DS}{field}{DS} .
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