My guest is battling to pay - apparantly he is asked for a coupon and he does not know where to get a coupon? I have never made a booking through Airbnb myself, so cannot advise him. Please assist.
Airbnb sometimes provides coupons to people (as a gesture of good will or as a marketing intrument), to be used as partial payment (discount) of a future booking. So if your guest does not own such a coupon, he should use a different payment method.