Conference calls can be made in below ways,
During an outbound call
During an inbound call
You can also move participants from a normally bridged call to a conference call
During an outbound call:
By making use of the HTTP call API https://www.plivo.com/docs/voice/detailed-reference/api/call/make-a-call/ an outbound call can be triggered by a number or an endpoint and when the dialed party answers the call the answer_URL of the API has to return a conference XML(like below) so as to put the dialed party to the conference room - My Room.
During an inbound call:
During an inbound call to a Plivo DID the answer_URL of the application attached to the DID should return the conference XML(like below) so as to put the caller to the conference room - My Room
From a normally bridged call to conference call:
The participants of a normal call can be transferred from the bridged call to a conference call with the help of transfer a call API(https://www.plivo.com/docs/voice/detailed-reference/api/call/transfer-a-call/)
To get the callUUID of the live call so as to record the inbound call, you can make use of these APIs
What is the maximum number of participants allowed in a single conference?
The maximum number of participants allowed in a single conference room is 20.