There has been a little bit of a buzz about this lately.
Pretty sure they are just gone for good. One person even reported having their account frozen as a result of using them recently.
Now the button has vanished entirely.
Looks like Audible just wants us to hand out the codes for review purposes.
Which is frustrating, since it is much simpler for a reviewer to accept a gift than to redeem a code. And of course, it allows the recipient to redeem the code for ANY audiobook, not just the one intended.
But I guess there isn't going to be a way to avoid that.
Can't see how it really helps Audible, so I'm not sure why they made the change. I guess, like most things, someone found a way to abuse it and ruined it for the rest of us.