Without looking @Kimberly419 , it sounds like you definitely have instant book on or a guest couldn’t have booked using it! But also, when you decided to pre-approve, you did not block the dates at that time. That then means the enquiring guest /s has up to 24 hours to take up your pre-approved offer, BUT, this is not set in stone, for the dates remained “open” for public viewing.
Therefore, first guest to book, is the winner!
Sadly though, by not blocking the dates at the time of sending the pre-approval, you don’t have control and you lost a day’s payment.
Pre-approvals can be sent to more than one person, but it is wise to let them know they are not the only one the offer has been sent to. Always let them know if the dates are still open, so they are aware, others can still book across the pre-approval time phase.