“Call Connecting…” Forever: Troubleshooting Video Chat Calls in a Cloudflare Tunnel

Problem Description
I have Element/Matrix Synapse/Coturn up and running on my home server for video chat. My ISP only allows port 443, so I’ve set all my services up to use Cloudflare Zero Trust. I can log into the video chat service using the mobile and web apps, set up rooms, and chat using instant messaging. Within the network, I can also use voice/video chat, but calls between servers ring but do not connect. As such, I believe the local configuration is correct and the Cloudflare Tunnel is at issue.

I have configured Cloudflare allow the needed ports for Coturn and established a network policy to allow Matrix users through the app’s required port. My tunnel’s private network is set to and the tunnel works for all other services.

To troubleshoot, I’ve tried putting the service on a subdomain (talk.domain.tld) and adding that to Cloudflare as a public hostname on the port required for Matrix. I’ve also tried moving the Coturn application in Cloudflare from self-hosted to a private network configuration. I’ve tried with Warp enabled and disabled. All the ways I’ve tried have the same result: instant messaging works, but voice/video calls do not connect.

Server running Debian GNU/Linux 12 (bookworm)
Element/Matrix Synapse/Coturn are all latest versions.
To eliminate conflicts, my router puts the server in the DMZ although my ISP blocks other ports.
Cloudflare is cloudflared and is latest version.
All services are go.