@Natalia699
This hasn't happened to me, but I just checked my coupons and the one I was awarded last year, which was due to expire at the end of this month is not there at all. I can see previous ones, e.g. the one I got the year before and redeemed, but there is no record of my last one. It's simply disappeared.
Yet another thing to have to call Airbnb about... as, like you, I doubt they will respond to my messages and then the coupon will expire in the meantime.