Unfortunately the site is not open to public. To reproduce it, you only have to request a booking that ends at the same day, as an already confirmed booking.
As you can see in this screenshot (https://ibb.co/myL5125), there is already a confirmed booking from the 20th to 22nd. When I request any other booking ending at the 20th, I get the error message “Something went wrong”.
Please let me know if I can provide any other information.