Searching for host... Connecting to host... Authenticating... Expected host key was not configured,

Hi I am getting below error when i run my bat script to automate the sftp file upload
script
script: open sftp://ex@ex.com/ -privatekey=ssh.ppk
lcd Z:\TR TEM DATA\
cd /home/cli/mm/gns ascii put -transfer=ascii -latest *.csv
exit
error
Expected host key was not configured, use -hostkey switch.

Can someone please advise

I've answered your duplicate question on Stack Overflow:
https://stackoverflow.com/q/51958491/850848