Are you using password-based authentication or SSH Keys to login to the server?
Are you using a PC or Mac (OS X / MacOS)?
If you're logging in from a Mac, then you'll need to specify the SSH Key when trying to transfer the files over.
scp -r -i /path/to/private_key /local/path/to/files email@example.com:/path/on/droplet
-r specifies recursive transfer, meaning all files and directories.
-i specifies the private key file using a direct path to its location.
/local/path/to/files is the local path to the files to transfer
root is the username of the user you're logging in as,
18.104.22.168 is the IP of your Droplet, and the
/path/on/droplet is where the files should be uploaded.
If you're not on a Mac, you can use PuTTy's
Alternatively, you could simply use SFTP. You can login as
root to transfer files, though you'd most likely need to set permissions on the files as you really don't want files and directories for your app to be owned by
root unless it's absolutely required for one reason or another.