If you are looking to create a new ticket when the customer responds on a closed ticket, it can be easily achieved with the help of automation rules.

Navigate to Admin > Workflows > Automations > Tickets > Ticket Update > New Rule and set up a rule as shown in the screenshot below

Webhook format

You can customize the content further and include other ticket properties as per your business requirement. Here is a sample query that can used to pass on ticket properties from the existing ticket to the new ticket.

"email": "{{ticket.from_email}}",
"description": "{{ticket.latest_public_comment}}",
"subject": "{{ticket.subject}}",
"status": 2,  
"priority": 1, 

Here's the link to our API documentation. For more details on webhooks, head to this article.