IIS 10: how to enable both HTTPS+HTTP bindings on one site to access the site from internet or local

Hi, I run an IIS web site having HTTPS binding for host name = "opendata.sperling.cz " at port 443. It is accesible from internet, as the name is revorderd in DNS and tehre is a rule in our router's firewall to reach the site. This is fine.
What I would like achieve is to be able to acces the site from local network or even localhost using HTTP port. I have added a binding without any host name using port 91, but it doesnot work.

I have tried to access it via http://localhost:91/ or http://192.168.10.20:91/, but non of it worked. It always redirected to https://localhost and disaplayed an SSL error, as the HTTPS host name does not match the entered.

What is wrong? Is it even possible?
Thanks.
Milan