Perhaps no one answered because of time zones, etc., @Michael378. It is just volunteers here. I know it is frustrating. Two more suggestions: First, look at your cut-off time for same-day bookings. Did the request to book come after the cut-off time? Second, it's your friend, so you can just block the date at this point. You probably have. I know you want to run it through the system, reviews and all that, but if the system doesn't cooperate, you just have to go with what works.
Hardly what you wanted, but hopefully it does get sorted.