The Service Category ID and Template ID (as) can be known by going to Admin > Service Category > select and edit the template:
{
"request": {
"subject": "Unable to fetch mails andresss",
"description": "I am unable to fetch mails from the mail server",
"requester": {
"id": "1807",
"name": "Requester"
},
"template": {
"is_service_template": true,
"service_category": {
"id": "1"
},
"name": "Request account deletion from Active Directory",
"id": "8"
},
"site": {
"name": "MSP Site",
"id": "2"
},
"account": {
"name": "My Org Inc",
"id": "1"
},
"status": {
"name": "Open"
}
}
}