The referrals program is no longer open and no new invites can be sent.
If you were sent a coupon prior to the shutdown of the program, you will be able to use the coupon on any booking made prior to the expiration of the coupon.
Sender credits will be honored till they expire. For prior referrals, you will receive credit upon completion of successful stay if the coupon is used prior to expiry (credit amount based on offer at the time).