That offer appears to only be through the invitation/referral system. It details the steps on how to invite a friend to the Revolut system.
You invite your friend and the invite link should allow them to get 1 free card. It’s not a free card to anyone that just signed up without being referred I believe.
I’ve not used the invite/referral system as it’s not very well advertised, neither are any benefits to it, so this is just my speculation and understanding based on the link above.
I got my first card for free during a promotion. Meanwhile I also got a second one. However, I think I had to pay the shipping both times.
Free card =/= free shipping. Free shipping is a Premium service.
You are selecting an option that is exclusive for Premium users. There should be 3 options and you have to scroll down and select the last one, which should be the free delivery card.