I need to provide my users with the ability to add a third person to their call dynamically. I know how to find the parentSid and the childSid of the call I'd like to transfer, but as soon as I update one of these sids to a twiml that contains the conference, the other sid is marked as completed and can no longer be updated. This means I can get either the first and third or second and third users into a conference, but I also drop one of the original participants.
I have tried the solution here: Twilio - How to move an existing call to a conference, but it seems to force me into the conference as soon as I dial the first participant.
I don't have the option of starting with a conference, and can't seem to update both ends of the original call. What am I missing? Thanks!