What is the requirement for an instant upgrade (with Avios) from Economy to Business?

- Do I need to book a certain Economy booking class?
- Does certain Business booking class need to be available?

https://www.finnair.com/de-en/finnai...-class-upgrade
https://www.finnair.com/de-en/info/t...and-conditions

I know this website, but no answers to my questions above exist. I do not want to be told only the waitlist is available