@Kathleen817 Hosts don't get to choose how and when an Airbnb guest pays. Long term bookings fall under the long term booking policies, which you should read.
Long term bookings pay the first 30 days upfront, then they are charged monthly.
But unless you are required to take only 30 day+ bookings in your area, it isn't advisable to take long term bookings through Airbnb- there are none of the safeguards a landlord would normally have when having tenants, and in most jurisdictions, a guest becomes a tenant after 30 days, subject to landlord/ tenant laws.
What if the "guest" who booked 3 months turns out to be objectionable? How would you plan to get rid of them?