Add your own Rapid API Key on line 46 of Script.js
Just go to rapidapi.com, search for ChatGpt has grab your API from GPT53
OR, just follow this link & have your API.
https://rapidapi.com/Glavier/api/chatgpt53
'X-RapidAPI-Key': 'RAPID_API_KEY',
If you want to use the official API from openai the instructions are provided within the code.