Buying Cyan from store (steam version)

I keep trying to buy cyan from the game. I click on the button to purchase $13.49 and in the top left hand side, it gives a Steamerror ; unable to launch steam and/or overlay to validate transaction.

What gives? Anyone know how to fix this?

[Chaps]

Hello, it might be because you unchecked the Steam option controlling the overlay :
Steam > Settings > In-Game > Enable Steam Community Ingame

It should do the job.