You pay at the time you book, @Omar587 . Then Airbnb holds that payment until the day after you arrive, when it releases it to the host.
So there is just no way you can pay a day late. You won't have a reservation if you don't pay when you book. You cannot stay with a host if you have not paid Airbnb.
Take a look in the Help centre to learn a bit about split payments and that sort of thing, but the best advice is to get your funds and payment method together before you even try to book a place to stay.
The good news is that there are no worries about fines, because fines are not necessary!