Currently this Blueprint is not available in the Store any longer, since it has a few errors that were supposed to be fixed. Instead, a system that allowed players to create their own Blueprints was implemented, and so it was captured and is now offered as a player made Blueprint in the Steam Workshop for Creativerse.
You can get the cornerstone for free.
Even if you have bought this original Blueprint once while it was still sold for Coins, then you cannot claim this old version any longer on any gameworld. The old Blueprint will only still be usable if you have claimed it already while it was offered, and only on this specific gameworld.