I wonder if someone else have the same problem like me. I'm just not able to use my superhost coupon to pay for any reservation! It says that the coupon number has been applied, but then it just doesn't allow to confirm and pay! This payment option strangely appears to be dead. It happened to me already twice. Like a month ago I needed to make an urgent reservation, but this coupon just was not applicable. I wrote a message to a support team, but got no reaction, so I had to pay with my card. And now it happens again! It all looks like some very bad trick. They grant you an award, but somehow you can not use it. It is so much disappointing!!!
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.