How to Warm Transfer Conference Call using Twilio?

I had read Twilio documentation about call transfer twilioDoc, StackOverflow and a lot of other stuff related to call transfer too. What I had tried is:

Step 1. Dial Call from web browser to phone number via javascript params. (call working fine)

params = {
    "PhoneNumber": number,
    "CallerId": "+1863201xxxx",
    "AgentName": "admin",
    
};
var connection = Twilio.Device.connect(params);

Step 2. Click the call transfer button and point it to the conference twiml

$conferenceId = $_REQUEST['callsid'];
$statusCallbackUrl = "https://example.net/Welcome/conference_control";
<Response>
    <Dial> 
        <Conference beep="false" statusCallback="<?php echo $statusCallbackUrl; ?>" 
          statusCallbackEvent="start end join leave mute hold" endConferenceOnExit="true" 
          startConferenceOnEnter="true"> 
            <?php echo $conferenceId; ?>
        </Conference>
    </Dial>
</Response>

Note: conferenceId is callID, the call already connected to the client

Step 3. I dial a participant to dial a conference

$participant = $twilio->conferences($_REQUEST['callsid'])
    ->participants
    ->create($caller_id, "+9230641xxx55"); 
// caller_id is the agent:admin (web client) and the phone number

The call rings to the phone number when he picks only the music plays.

Twilio conference call has only 1 participant don't know why? Why the first active call not converted to a conference call, if not possible then how it will be?