i got an answer:

"If you're sure the key hasn't been redeemed elsewhere, please have the friend sign out of Steam and close out of it completely (ending the process in Task Manager/Activity Monitor/System Monitor). Then tell them to reboot the client, log back in, and try to redeem the key once more.

If you continue having trouble, please update this ticket with a screenshot of the error they encounter when trying to redeem the key."

could you do that please?