I bought all those keys from GreenManGaming store. I will ask their support if they accept to replace your key. Wait and see.

Just got a replacement key. I'm changing the sent key serial.

Thank you for getting in touch with us.

I'm sorry to hear this, I understand the issue you are having and as such I have sent this key off for deactivation and investigation by the publisher and Steam.

So that we can serve you best, I have now assigned a new key to your account and you should no longer have any issues.

Your new key is available in your GMG account.

Please let me know if I can assist you any further.

Kind regards,
Josh

Customer Support
Green Man Gaming

Sorry for that but probelms comes from GreenManGaming. I bought 6 keys (3 were good, 3 already in use)
Even their last replacement was duplicated.
I will contact GMG support and ask them to fix this mess by replacing already used key.

For your information, GMG support was able to provide a working key (after 2 tries!!!!) for this one
https://www.steamgifts.com/giveaway/FERSk/deck-casters
Hopefully you will be next soon. Ticket for your already used key is "under query".
So now 5/6 were delivered and activated.
I hope to contact you soon with a good key.
Bye

OK key has been mofified. Let me now if it works or not