chatgpt api 무료버젼 연동해서 사용할때 용량 에러 뜨는 문제

<?php

$openai_api_key = 'sk-***';
$text_prompt = 'Once upon a time';

$curl = curl_init();

curl_setopt_array($curl, array(
  CURLOPT_URL => 'https://api.openai.com/v1/engines/davinci-codex/completions',
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => '',
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 0,
  CURLOPT_FOLLOWLOCATION => true,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => 'POST',
  CURLOPT_POSTFIELDS =>'{
    "prompt": "'.$text_prompt.'",
    "max_tokens": 5,
    "n": 1,
    "stop": "."
  }',
  CURLOPT_HTTPHEADER => array(
    'Content-Type: application/json',
    'Authorization: Bearer '.$openai_api_key
  ),
));

$response = curl_exec($curl);

curl_close($curl);
echo $response;

?>