stay postponement

In an e-mail received from BOOKING on the new measures taken because of Covid-19.
I read: "our GCP allow customers to cancel or postpone their stays".
However, I received a request for postponement from customers.
They wish to come in September, but they inform me that on BOOKING, no available dates appear in September whereas I still have some dates available.

Why can't our clients postpone their stay?

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