Restrictions Against Extending a Reservation
A reservation cannot be extended if the rate amount for the number of guests (adults and children) does not exist in that rate. The amount per extra adult/child can be 0.00 but cannot be null (i.e., blank). You will receive the following error message if you do not enter a rate amount: "Rate amount is unavailable for this occupancy. Rate amount is not a number." This is because null is not a number. A null value cannot be used to calculate the rate.
To learn more about extending a reservation, see this article.