rest chat api error

Summary

its giving internal error please help me fix it

Code Snippet

<?php

$curl = curl_init();

curl_setopt_array($curl, array(
  CURLOPT_URL => 'https://xxxxxx/services/rest/crossChannelServices/v1.4/establishSessions',
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => '',
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 0,
  CURLOPT_FOLLOWLOCATION => true,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => 'POST',
  CURLOPT_POSTFIELDS =>'{
    "sessionInformation": "{\\"emailAddress\\":\\"[email protected]\\", \\"firstName\\":\\"Ruman\\", \\"lastName\\":\\"Nisar\\", \\"question\\":\\"Test Chat\\", \\"auxiliaryData\\": {\\"BROWSER\\":\\"Firefox\\", \\"OPERATING_SYSTEM\\":\\"iPhone OS\\", \\"USER_AGENT\\":\\"Mozilla/5.0 (iPhone; CPU iPhone OS 11_4_1 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/11.0 Mobile/15E148 Safari/604.1\\"}}"
}',
  CURLOPT_HTTPHEADER => array(
    'OSvC-CREST-Application-Context: chat-api',
    'Authorization: Basic ',
    'Content-Type: application/json'
  ),
));

$response = curl_exec($curl);

curl_close($curl);
echo $response;