The Flat File Connection Manager can be used with the File Transfer Task for the Local parameter when the Action is Send Files. However, it cannot be used when the Action is Receive Files. In that case, a File Connection Manager should be used.
If you are using the Send Files Action, then the only parameter that is used in the Flat File connection manager is the ‘File name’ parameter. When you set up the Flat File Connection Manager, browse to the folder where the file(s) are located and choose a single file.
If you wish to upload more than one file from that folder, you can re-open the Flat File connection manager after closing it and remove the file so that the ‘File name’ is pointing at a folder containing multiple files. This will also work with the Send Files Action of the File Transfer Task.