You can opt to setup your own TURN & STUN Server if you don't want to use any third-party services.

First you have to get a Server to setup your TURN Server.

Read this for minimum server specification required for TURN & STUN Server:

https://kodemintserviceshelp.freshdesk.com/support/solutions/articles/81000319096-what-is-the-required-server-configuration-

Coturn is a free and open-source implementation of a TURN and STUN server for VoIP and WebRTC.

Its available at https://github.com/coturn/coturn

Here are reference articles on how to setup TURN Server with Coturn:

https://www.webrtc-experiment.com/docs/TURN-server-installation-guide.html#coturn

https://nextcloud-talk.readthedocs.io/en/latest/TURN/

Once installed you get TURN/STUN server url and credentials, you can go to Configuration -> ICE Servers configuration on the app and put the required details.

Or you can hire us to setup STUN/TURN Server for you.