Originally Posted by
maclover
Just book a prepaid reservation for the first two nights and than a best-flexible for the last one.
Remember that the certificate covers the SECOND weekend night of your stay. If you stay Friday, Saturday, Sunday, then Saturday is your free night as this is the 2nd night of the weekend (which IC treats as Fri / Sat / Sun). You should therefore book Fri and Sun on Advanced Purchase and Sat as Best Flexible. You end up with 3 separate bookings but it can't be helped.
If staying Thu / Fri / Sat, you would book Thu & Fri together as Advanced Purchased and Sat as Best Flexible.