Hello!
I tried sending you Don't Starve together gift from steam gifts, but it looks like you are not accepting the gift.
Can you please do so as 2 weeks passed and I'll need to change to another winner?
Thank you!

Hi, about your barter dispute, AER HB keys have a high rates of duplicate code errors, this already has been reported 10 months ago. In Notices you will see duplicates info https://barter.vg/i/21151/ , https://www.steamgifts.com/go/comment/XPNdAHb

You can contact with Steam support by opening a ticket and sending a message asking them in a polite way that you tried to activate a key (provide them with the key) and that it gave you an error message that it was duplicated and if they could please tell you when it was activated or if it was revoked by developer.

Then, if support provided you with this info, you will have a valid and solid proof about the key you received was already used or revoked by developer before the trade with the other user became effective.

Then, include to the barter trade conversation a screenshot with the message you received from Steam support and ask to a barter mediator to check your proofs so you get the dispute removed from your account.