element-call/config/element_io_preview.json

{
  "default_server_config": {
    "m.homeserver": {
      "base_url": "https://call.ems.host",
      "server_name": "call.ems.host"
    }
  },
  "temp_sfu": {
    "user_id": "@sfu:call.ems.host",
    "device_id": "YNZDLSEQMP"
  }
}