When booking, the option of free cancellation is displayed, but I can not complete the booking without entering credit card information or pro forma invoice.

Before booking, you need to check the date of validity of free cancellation on Terms of Cancellation link.
In most cases, it is necessary to make a deposit at the time of booking in accordance with the payment terms. In case of cancellation of booking in the period when the cancellation costs do not yet apply, a deposit made is transferred to a new booking or returned to the payer.
In case you pay for the booking directly in the accommodation without a deposit, the credit card entry is required as a guarantee of your arrival. In case you cancel the booking at a time when the cancellation costs are already valid or if you do not arrive on the scheduled date of arrival, the cancellation costs are debited from the card.