WebRTC is not working without HTTPS. If user is on unsecure page, microphone will not be granted by browser.
Option1
Try to purchase a domain name like streaming-local.com and add DNS A record
192.168.1.22 streaming-local.com
Here 192.168.1.22 is WCS server in your LAN.
Then purchase SSL certificate for this domain and import into WCS server.
Option 2
If external DNS is not reachable in your LAN due security constraints, spin up LAN DNS server (like bind) and add the same A record
192.168.1.22 streaming-local.com
So this is an admin task to setup local DNS properly. Anyway, server must have a FQDN(valid domain name) and SSL certs imported.
Option 3
You can import Self Signed SSL certificate without domain to all user's browsers. So if you have 100 users, you have to open browser preferences on each user machine and import this certificate manually, or publish similar corporative instruction. Looks too complex than just setting up valid domain once.
Option 4
The same as Option 3. Just add /etc/host record on each user machine. Then you will be able to use local domain without any DNS server.
192.168.1.22 streaming-local.com