Free games are available for free, you can’t run a promotion on them since they aren’t purchasable.

If you want to grant someone ownership of the game you can generate a download key for them manually from the downloads key page.

Based on reviewing your comments section, a single account was asking for you (and many others) to change how your game is distributed so they could “claim” a copy of the game. This is against our rules so we’ve issued a warning on their account and removed the post.