@Nancy880 You say the guest has a confirmed reservation. The dates get automatically blocked for a confirmed reservation and the guest has 24 hours to pay. I don't understand what you mean about blocking the dates manually.
I wouldn't block dates for a guest who didn't have their payment together. First come, first served. You could have lost out on other bookings and the original "waiting for payment" guest never books at all. Don't be so nice 🙂
And guests don't pay a "deposit". Their booking is paid for within 24 hours of booking. They can opt to pay in 2 installments, but that's between them and Airbnb.