problem with date range in booking availability

I manage a tourist website, I’m trying to set up a product bookable only during a week in April.
in product panel, in availability tab, I set “all dates are: not available by default” and “check rules against: all blocks being booked”
then I add the range type date range, with the specific week in range, bookable: yes and priority : 1. there are no global availability rules.
but still when I preview changes, that specific week in calender is grayed out. I checked different setting, tried making it available by default and then ruling out all times except that week (rule didnt apply) also tried adding range of days after date range. all to no avail.
what could be the source of problem?