how to use multy select custom field for filtering

-- HikaShop version -- : 2.3.4
-- Joomla version -- : 2.5
-- Browser(s) name and version -- : FireFox

Hello
I want to use a multy select custom field for filtering products in a category. The problem is that when i add a new filter for my category and apply it on custom fields, i can not see a list of my custom fields to select one.

I found my mistake.
I didn't choose the correct category for my filter so i couldn't see custom fields