@Bill329
"To qualify for any payouts, the Referred Host’s first received booking must have a value (excluding cleaning fees, taxes, and special offers) of at least $100 USD (or the equivalent in your local currency ). The Referred Host has 150 days from the date they are invited to Complete their first qualifying booking in order to earn the Payment."
https://www.airbnb.com/help/article/1129/host-referral-program-terms-and-conditions---referring-host
I believe if their first booking does not meet these requirements and their second one does, the entire reward offer is nulled.