Hello Lim,

This appointment booking is been used by Walkin experience & Field service management as well. I think this below link can guide to crack some information you are looking for to work on API. this B

https://community.servicenow.com/community?id=community_question&sys_id=d944b503db8da0107d3e02d5ca9619bb

As mentioned, Go to REST API Explorer and select the appointment table and check the POST request. There you get a sample script, which you can then use it in your instance.

Regards,

PaulSylo
Community Raising Star!