@Heather64 Airbnb is not a good platform for hosting long-term guests as many hosts have found. One of the most obvious reasons is the cancellation/alteration of reservations.
For a standard leasing agreement, a landlord can get one month deposit and last month rent when a lease is signed by a tenant. Anytime a tenant breaks the leasing term including the early termination of the lease, the tenant will lose the security deposit and last month rent at least. In some case, the landlord could pursue the rent for un-rented days after a tenant terminates the lease early.
When a guest book long-term (>28 days) through Airbnb, a long-term cancellation policy applies. As @Anonymous mentioned, you could only get paid for 30 days after the cancellation date.
For example, your guest booked 90 days between August 1 to November 30. If he stayed between August 1 to August 31 and asked for alteration and would leave on September 1, you should not accept the alteration to end the booking on September 1. Instead you should have asked the guest to cancel on September 1. Then you would have got 30 days payment between September 1 to September 30. And your calendar would have been open since September 1. If you had accepted the alteration to end the booking on September 1, you would not have had the extra 30 days payment.
If your guest did not cancel or terminate and continued to stay till September 30, you would have get paid for the entire 90 days.
I am not clear about what you said that your guest was still staying and did not have the calendar open.