Hi,
Could you provide a screenshot of the settings of your filter, if you're using a filter module for the display of the filter, a screenshot of the settings of the module, and the URL of the page where the filter is so that we can look at the situation ?
The most likely issue is that you're using the filter module, but in your module settings, you either left the "menu" setting empty or you entered a wrong menu item id. You need to enter in there the id of a menu item of the type "HikaShop products listing" which is configured to list all your products by default so that the filtering can be done on that list.