How can I make my Apple ID eligible for recovery key?

Hi,

I have 2 apple accounts: one is the main Apple ID on my iPhone and Macbook, and has a recovery key setup. I use a second apple account just for an email. The second account is installed in both my Macbook and iPhone. I am trying to create a recovery key but i get a message "apple id not eligible for recovery key".

Does anyone know how fix this? Thank you!

[Re-Titled by Moderator]