4-way conference on VVX450

Hi,

I have a VVX450, firmware 5.9.1 (latest as of this post). I am looking to do a 4-way conference.

- I have feature.nWayConference.enabled="1"

- When I join the first two participants, I do have a "manage" button to mute participants (if I understand correctly, it means nWay is indeed enabled.

I just don't know how to add a third one. I do not get the "conf" option anymore at that point.  What's the exact key sequence to add a fourth participant?