Plugin: Search & Filter

Good afternoon
please help me to understand what is going wrong?
have a web-site of my copany rlight.by
have a categories (catalogs f.e.)
when I choose one category (f.e. architectural lighting – everything works correctly)
https://www.rlight.by/category/architect/

when I choose two or more categories – nothing wrorks
https://www.rlight.by/category/architect+decorative/

we see + between architect and decorative tags and 404 – File or directory not found.
but if we replace manualy + for , in URL – everything works correctly
https://www.rlight.by/category/architect,decorative/

please help me to solve this question

Br

The page I need help with: [log in to see the link]