Element Web calls don't work if /thirdparty/user/im.vector.protocol.sip_virtual is not implemented

[timokoesters]

Steps to reproduce

1. Connect to Conduit homeserver
2. Start a voice call
3. See this request fail in devtools:
   GET https://matrix.redacted.com/_matrix/client/r0/thirdparty/user/im.vector.protocol.sip_virtual?native_mxid=@testuser2:REDACTED.com

From web to android and android to web. (both users on the same conduit server)
If web calls android, CORS error (because /thirdparty is not implemented). Nothing happens UI wise.
If android call web, on android I hear the ring, on the web I see "Missed call" automatically, android keeps ringing until I hang up

[timokoesters]

(There has been a misunderstanding, can someone migrate this issue to element-web?)

[bmarty]

I cannot transfer the issue to element-web (probably because I am not an admin of eleweb project anymore). I will ask someone to do it.

[vi]

Is there a workaround available?
I.e. some easy modification of Element Web or a backend server that allows the call to proceed?