I haven't used that node, but always, when you have trouble with a node, the first thing to do is to look at the data you are sending to it. Feed the message that is going into the sftp node into a debug node and show us what is there. That is more important initially than showing us the code in your function.
[Edit] In the node you don't seem to be setting a working directory. Also I would advise against using ./ at the front of the file path. There is no need.
[More Edits] It may not be valid to specify a path for the remote file, it may be that only a file name is allowed. Try that first to get it working.
Also, if you look at the issues against the node you will see that none have been answered for a long time, and several of those issues are serious. The conclusion is that the node has been abandoned. You may have to find an alternative way of doing it.
As I already said, it is not clear that you can specify the folder with the filename. At least for the moment, to see if the node works at all, put the folder in the node configuration and just feed the filename and data in. Look in the help text for where they have to go and check you have it right. There is no point posting screenshots of flows, code or errors until you have got the data in the debug node matching what the node asks for.