Here i explain about how to upload file on FTP server
You need to buy FTP extension.
[PAID] FtpClient: An extension to communicate to remote server [$5 or INR 350] - Extensions - MIT App Inventor Community
Need Hosting for storage.
set all conetion like user id, password, port = 21, file type = 2 & server name.
connection is ok than take upload block see below image.
Watch Video easy to understand