Nextcloud talk mobile (ios android) app problem with TURNs (ssl) protocol

Hello, everybody! After full install and config all of required applications (nextcloud, signaling, turn-server, etc.) in standalone version for using Talk (spread) app, it is impossibe to establish TURNs-protocol (ssl) connection with mobile-clients and others.
Turn servers always throws denies (coturn and exturnal), like: Connection failure: SSL_do_handshake failed: error:0A000418:SSL routines::tlsv1 alert unknown ca
(or error:0A000416:SSL routines::ssl/tls alert certificate unknow - with self-signed try)
I have tried many others certificates includuding self-generated - always the same answer. I’ve tried to dig GitHub - nextcloud/talk-ios: 📱😀 Video & audio calls through Nextcloud on iOS but didn’t find answer in the code.
Meanwhile, web-browser’s client on mobile device connects fine as well as windows nc-client works fine, but ios and android apps throws this “0A000418 unknown ca” error which ruins all my afforts, unfortunately.
Does anybody handled these question?

UPD: debugging with adb the android talk app gives the following error, but still not to much to get the reason.

adb logcat -s chromium:

chromium: [1013/133712.534541:ERROR:net/socket/ssl_client_socket_impl.cc:900] handshake failed; returned -1, SSL error code 1, net_error -100

As long as you don’t use a valid SSL certificate, you will run into trouble with invalid SSL certificares from time to time.

Install Letsencrypt for your Nextcloud and subdomains you are using on your server.

im using exactly letsencrypt certificate (with fullchain and priv.key, actually i’ve tried all of them) you’ve mentioned and the problem’s described above