Mobile cannot connect to my local jitsi server

I install a environment in a lan refer to https://github.com/jitsi/jitsi-meet/blob/master/doc/quick-install.md.
I can start a call in my laptop,but cannot connect to the meeting using my andriod phone.

jitsi server url is https://172.20.63.18/

For mobile you need a trusted certificate, like Let’s Encrypt, which will not work with and ip address.

Thanks for you reply @damencho.

Certificate is difficult for me.
Who know the src code of andriod app downloaded from https://jitsi.org/downloads/