Twilio conversation to Conference call from Simple call

Question

I want to add users to simple call generated using twilio to update it to conference call

 public function forwardCallToUser(Request $request)
    {
        $client = new Client($accountSid, $authToken);
        $conferenceName = 'Conference_' . time() . '_' . rand(1000, 9999);
        $newUser = User::findOrFail($newUserId);
        $newUserNumber = $newUser->phone_number;
        $call = $client->calls($ongoingCallSid)->fetch();
            $twiml = new VoiceResponse();
            $dial = $twiml->dial('');
            $dial->conference($conferenceName, [
                'startConferenceOnEnter' => true,
                'endConferenceOnExit' => false,
            ]);
            $client->calls($ongoingCallSid)->update([
                'twiml' => $twiml->asXML()
            ]);

            $message = 'Converted existing call to conference and added new participant
        return response()->json([
            'success' => true,
            'conference_name' => $conferenceName,
            'new_participant_sid' => $newCall->sid,
            'message' => $message
        ]);
}

it is giving me error

"[HTTP 400] Unable to fetch record: Invalid CallSid: CH8284f315ba6e43f1822e4efec9708bd1" even though ongoing call sid is same as mentioned above

I want to integrate adding user to simple call and make it conference call using twilio