IS SSH host key fingerprint IS mandatory for Watching for changes in SFTP/FTP server

I want to watch for changes in the SFTP/FTP server and download the file. when I run the code it says that SSH host key fingerprint is needed.is that mandatory?

It's better if you use one. You do not have to if you do not care about security.
See https://winscp.net/eng/docs/ssh_verifying_the_host_key#automation