Please provide more details:

• version
• steps
• which party initiated call
• what was the outcome - any errors? catlogs will be welcomed.

3.0.27.f and 2.8.3+fdroid Call then pickup, both ways Black screen after pickup

Can't log anything now, today Stork does not appear as online for Conversations, they can exchange messages (broken OMEMO but that's another issue) just fine otherwise, but there's no Video call menu entry (Stork sees the contact as Away) and no call icon in Conversations (contact is shown as offline, dark send icons).

One possible issue is that Stork does not support extdisco:2 so it tries to connect to (the hardcoded) Google for STUN, which is not allowed.

My server provides both STUN and TURN, and these should be used.

@licaon-kter Why it's not allowed (you block those?). That would explain it as XEP-0215: External Service Discovery is not supported for the moment.

Yes, also STUN only is a special case, in my testing with Conversations TURN was always used.