I remember when I activated a previous Frozen Synapse Prime key, it gave me an extra gift copy in my Steam inventory. I don’t know if this is still the case, though I would imagine they probably haven’t changed it. Though that was quite a ways back, so I cannot confirm that, perhaps someone who gets a new key without having it in their library can comment?
GMG first tells me my account doesn’t exist, but it logs me in anyway. Giving me access to my account details and previous purchases but when I try to hit the “get your free game” button it still tries to make me login. I add the game to the cart anyway and now all of a sudden the coupon code becomes visible, but the game shows up as out of stock.
I’m getting the same out of stock error as you. Logically, I know they’re referring to game keys, but it’s still silly to think about a digital game being “out of stock”… Somebody call the internets and tell them to manufacture more 0s and 1s, greenmangaming is plumb out of 'em!