Searcg by category

Hi,

I have installed “search by category” plugin on my webiste. I downloaded it from: https://wpadverts.com/documentation/creating-ads-list-adverts_list/.
When I try to search I got 404 error. I have saved permanlinks and updated plugin to the newest version.

Please help me !

P.S. It is great plugin ! Thank you !
Here is a link to my website ! http://www.letspace.pl