@Jen7132 You have to give more specific information in order for anyone to be able to give you an on point answer. How long did this guest book for? If it is a long term booking, you will be paid monthly. So if the guest booked for 2 months, you would get the first month's payment after theey check in, and the second the following month.
If it's a short term, there is no way a guest can check in without having paid the full amount. If they opted to pay in two installments, if they didn't come through with the second payment, Airbnb would have cancelled the booking.
In any case, if there is a payment question or issue, you don't start by confronting the guest- you contact Airbnb, as they handle the payments.