Correct me if i'm wrong, but doesn't it state that no form of items maybe bought or sold, free or not, or even advertised? I think you should check this.
Here's the rule that you're citing.
Advertising / Soliciting / Trading
- You are expected not to advertise third party products or services on our boards.
- You are expected not to solicit services, paid or free, on our boards.
- Our forum is not a place to barter, trade or illegally transfer funds, in-game content, or products.
Link to full rules: Community Etiquette & Guidelines
The OP is simply giving it away. We don't want people trading or buying content though. That quickly becomes an issue, but a code that he has left over and isn't charging or trading for isn't a big deal. We'll expand on giveaways and such in the future to make it a bit clear.