How did you "encode" your sheet music

As I already have a quite a few printed and sitting in boxes, I simply encoded a largish sticker and slapped it on the book for all new sales. I also sent an email to all my customers telling them about this new feature and provided a link in the email so all my past customer could take advantage of engaging with me.

When I print a new version, I’m going to include the tech in the front cover so a sticker won’t be needed.