How can I transfer a file over SFTP using Cyberduck?

Hey all! I setup an SFTP and generated and used PuTTY Key Generator for the SSH Public key. As per guidance on the AWS site for transferring a file, I downloaded Cyberduck and followed the instructions. I pasted the endpoint into the 'Server' field. used 22 for 'Port number', entered my username, and pasted my SSH private key. However it also asks for a password. The only password i recall setting up was the one for the public key, however when i enter this and select 'Connect' in Cyberduck, i receive the message "Listing Directory Failed. Failed to create user (Unsupported or invalid SSH public key format)". Can anyone advise what i'm doing wrong please? Thank you!