I need request body writing for API link

Description

I want to create a function on Intercom, for the chatbot to be able to book a table on our reservation software Guestplan. I am struggling to write the 'Request Body'. I need this writing.I've included a screenshot of the page on Intercom.
The link to the API documentation for Guestplan is here: https://docs.guestplan.com/#/api_referenceThe link to the Swagger JSON file is here: https://www.etender-connect.com/v1/specs/swagger.json
The API is linked, the authentication is working correctly.
I just need somebody to write the relevant command or provide guidance, testing by me is then quick.