You are unable to check out an order that has not been paid.
In order to get end of day reports, all bookings must be checked out so that revenue can be pushed to your PMS system (if you have an integration set up - see guide on the integrations available), so this is very important.
There are multiple ways to check at the end of the day if all Orders have been Checked Out and accounted for:
Head to the Home dashboard > open the Daily Revenue report > Orders > scroll through the Orders and check that they all have a status of "Settled"
Head on to the Calendar and scan for green tabs on all bookings
Head to the Orders tab > Filter item to date to Today > Check that all orders have a checked out status.
You are able to check a guest in before payment, but no option for Check out is visible until the booking is paid for.
You also won't be able to check Orders in or out until the day of the Order.