Can I show my customer the cancellation policy and the free cancellation date before they pay for a hotel?

Yes, in almost every case you can show both before your customer pays. Most hotel booking APIs send the cancellation terms along with the room price, either in the search results or at the pricing step just before payment, so your portal can display the free cancellation date on the room card and repeat it on the payment page and on the voucher.

How much detail you get depends on the supplier. Some send a clear deadline together with the amount that would be charged after it, some send only a short sentence of plain text, and non refundable rates simply state that nothing comes back at any stage. Treat the policy as belonging to the exact rate your customer picked, not to the hotel itself, because the same hotel on the same night can offer a flexible rate and a cheaper non refundable one.

Two things catch agents out. The deadline is normally in the local time of the hotel, so a cancellation that looks like it was made in time from your side can still arrive late at the property. The terms are also fixed at the moment of booking, so rely on the policy stored with that booking rather than looking up the live rate again weeks later, because the hotel may have changed its terms since.

Before you go live, make one test booking on a flexible rate and one on a non refundable rate, and check that what your customer sees on screen matches what the supplier sent, and that the same wording reaches the voucher and your own booking record.