I can not connect to jitsi with the Android app

i have ubuntu 18 and local server in my Lan.(server is and clients is
everything is Ok and only can not connect to server with the Android app in local Lan.Mobil’s connect to server by access point.(DHCP IP).
Please guide me.

Have you installed let’s encrypt certificates. Mobile requires valid certificate in order to work.

Thanks for your response.
I don’t know enough about it.
Please advise more.
Where to download and how to install?

For this to work you need a working DNS that is used for your deployment. If you are just using ip-addresses it will not work. Then you maybe able to use mobile devices if you get the certificates that are used and transfer it to every mobile device that will be using it and install the certificates there.