If you can't pay the second stage payment that you committed to paying for by an agreed date @Kiaraliz0 when you booked -
Airbnb will cancel the booking and you will lose the first part of the payment so you would be better finding a way of making the payment for example on your credit card/borrowing from family/friends.
As @Helen3 has said, here's what I could find in the help article:
If the second payment of your payment plan doesn’t go through, we’ll let you know and ask you to make the second payment right away. If you’re unable to complete the second payment within 72 hours, your reservation will be canceled—any refund for the first payment will be determined by the cancellation policy for your reservation.