In response to the email, this has solved my issue and I have been able to activate Song Sergeant.

Thank you for taking care of this for me, and thank you for a decent little app.

I sent an email to songsergeant@lairware.com as instructed from your website a few hours ago, using the same email address that I used for Kagi, what else do you need?

Purchased SongSergeant via Kagi, received confirmation email and Key Code but cannot activate. Deleted plist still no joy. What now?